TEST AND MEASUREMENT

2.4 GHz Spectrum Analyser-CYM6935 Module

noreply@blogger.com (Go2Media) — Mon, 13 Jul 2009 04:07:00 +0000

There many wireless devices available on the market now that broadcast in the 2.4 GHz spectrum including Bluetooth, 802.11a/b ethernet (WiFi), Zigbee, wireless USB, cordless phones, wireless mice and keyboards and the humble microwave oven. Depending where you live in the world your government has allocated a roughly 80 MHz block for transmitting all manner of data starting at 2.4 GHz. It's getting a bit crowded in this band, especially if you live in a built up urban area. With this project you can monitor what's going on and figure out what channel to change your WiFi network to in order for it to keep working when your neighbor rudely sets up their wireless network on the same channel as you (that'd be channel 6, you lazy sod).

How to do it? Quite a few companies are now making 2.4 GHz data transceivers crammed into a single chip. These chips are very cheap but pack quite a bit of functionality. One thing they have in common is an RSSI (Receive Signal Strength Indicator) register that lets the chip monitor how much signal power it's receiving. In practice before the chip transmits it's generally a good idea to spend a few milliseconds listening to see if there is anything else broadcasting on the same channel. If the RSSI level is below a certain level it's safe to assume the channel is clear to transmit on.

Taking advantage of this RSSI register allows one to construct a crude but effective spectrum analyser. Cypress Semiconductor make a range of 2.4 GHz transceiver chips intended for short range use such as wireless keyboards and mice. The chip CYWUSB6935 contains an RSSI register with 32 magnitude levels. It also has a radio that starts at 2.4 GHz and is tunable in 1 MHz steps. Unfortunately the chip comes in a "QFN" package with the pins secreted away under the casing of the chip. This make it impossible to hand solder. Fortunately Cypress saw fit to produce the CYM6935 module - it's a little circuit board with the chip, support components and antennas conveniently integrated together. All we need to add is a parallel port, power and software to read the RSSI and see what the pesky neighbor is up to.

2.4 GHz Spectrum Analyser Components
- CYM6935 Module - Can be obtained from Cypress as a sample or purchase through their website and distributors
- 4 10kohm resistors
- 4 15kohm resistors
- 3 silicon diodes
- Ribbon cable

- Male DB-25 connector and backshell
- Hookup wire
- Prototype circuit board (such as Veroboard or a ready made PCB from Elektor
- USB cable (for power only, not data)

2.4 GHz Spectrum Analyser Construction

The CYWUSB6935 is a 2.7V to 3.6V device. The three diodes are designed to drop 5V down to about 3V. My PC PSU only puts out 4.7V so I am using only 2 diodes to get 3.3V. I originally tried to wire all 8 data outs in parallel through a diode each so I could turn the device on and off from software. The current wasn't anywhere near enough in spite of the data sheet for the I/O chip on my motherboard claiming to be able to. As an alternative I chopped up a USB cable and derive my 4.7V from the USB supply. You could be a pedant and use a 3.3V regulator instead of some diodes.

The resistors divide the signal output levels from TTL to 3V CMOS compatible levels. The parallel port is TTL compatible so the 3V signals from the chip can directly drive the parallel port signal inputs.

The module itself uses a header with a 2mm pitch which isn't readily available from your local electronics shop. You can see in the photo below I had to improvise with a cutout, bent wires and bluetack to mount and connect the module onto the main board.

2.4 GHz Spectrum Analyser Software
The provided QTScan Linux and QTScan Windows software I have written is a basic driver and display for the CYWUSB6935. It is a QT application written to run under Linux and Windows. Little or no tweaking of the parallel port driver may mean it will also work in various BSD's and OSX (with a USB-Parallel port device). The QT viewer part shouldn't need changing under any platform.

Building The Software
To build the software ensure you have the QT4.x development and runtime libraries and kernel headers installed. I have already supplied a binary that should work on an Ubuntu Feisty based system. Otherwise, simply run make to build your own copy.

The parallel port driver is a bit banging SPI driver. I have designed it to work in standard (SPP) parallel port mode and have set my BIOS to force SPP mode. The driver also initialises the chip and also provides the scanning function.

The scanning function starts by setting the radio frequency channel to 0. This sets the receive frequency to 2.4 GHz. The RSSI value is then read and the channel number incremented. Each increment corresponds to 1MHz step and a complete scan ends at 2.483 GHz. The radio can go a bit higher but there isn't much point as it's outside of the ISM band. The chip obtains an RSSI value by taking a snapshot of of power levels at the channel in question for 50 microseconds.

By taking successive 50us snapshots of each frequency a complete scan is performed. Unfortunately, reading and writing the parallel port is a very slow process as the port hardware deliberately runs at only several hundred kHz for historical and compatibility reasons. On my system I measure about 600,000 ioctls/sec can be performed. This means that the inb and outb instructions when accessing the parallel port are stalled for a very long duration compared to the clock speed of the CPU. You will notice because of the instruction stalling the System load will peak at close to 100% when running qtscan. In spite of this I get about 23 scans/sec which is a useful speed. The SPI port on the radio chip can run about 10 times faster than what I am able to do with the parallel port - this would translate to well over 200 scans a second. This could be achieved with a dedicated GPIO or SPI port as found in many embedded microprocessors.

You can run qtscan even without any of the hardware as the program blindly drives the parallel port. The scans/sec result upon exiting should be in the low 20's,

The parallel port driver and hardware provide a good start into getting this module to do data transmissions as well as performing the trivial RSSI application.

Results
The qtscan application will display the current scan as a red line. Absolute peak levels are displayed as green bars behind the red line. The ticks on the x-axis are each channel at 1MHz intervals. The span is from 2.4 GHz to 2.483 GHz. The yellow lines are the 13 802.11b channels. The y-axis ticks represent the 32 levels from the RSSI register. Unfortunately I haven't been able to calibrate what each magnitude tick translates to in received power dBm. The data sheet says RSSI values in the range of 28-31 are -40dBm and 0-10 are <-95dBm. I don't think it's a precision measurement nor did Cypress intend it to be.

Because each scan only takes successive 50us snapshots the program needs to be left running to collect peak magnitudes. This peak magnitude plot builds up to give a good indication of the bandwidth and relative magnitude of a signal under observation.

Image 1: This shows my microwave oven about 5 metres away merrily spamming a greater portion of the 2.4GHz band. This was a 50 second observation.

Image 2: This shows my access point centred nicely on channel 9 using 802.11b. You can see how the spectrum bleeds over into the adjacent channels (which is fine). This is a 2 minute observation of just the beacon and associated chatter from the access point with no actual data being sent. The magnitude peaks at maximum level (31) which is no surprise as the AP is only 2 metres away.

Image 3: This shows what I suspect the beacon carrier from a 2.4GHz phone next door at centred around 2.411GHz. I have observed it to jitter and even disappear on occasion but it's usually present. My /proc/cpuinfo says my Athlon's internal clock is at 2.31GHz so I don't think it's my computer.

Image 4: This shows shows the sudden burst of traffic from my USB Bluetooth dongle (about 1m away) when I ran the KDE OBEX client. It must be a broadcast of some kind. This scan lasted about 10 seconds.

In all the images the overall noise floor occupies the first 7 or so levels which I think is a function of the device.

Source: DIY 2.4GHz Spectrum Analyser

Simple RF Probe

noreply@blogger.com (Go2Media) — Fri, 31 Oct 2008 17:18:00 +0000

This simple RF probe can be used to determine if the oscillator is working. It will not tell you the frequency (you need a good RF frequency counter for that), but at least you will know if it is oscillating or not.

This RF probe is useful for any low level RF work, and simply connects to your multimeter. The voltage shown will not be accurate, since this is a rectifier probe, but the measurements are good enough for you to be able to determine where the RF stops, or if a stage is not giving the gain you think it should.

Connect it up to your multimeter, which can be used on any suitable voltage or current range, or you can use a micro-ammeter if you happen to have one lying about. For use with lower frequencies (a few MHz only), C1 can be increased in value, but I would not go above 100 pF. High voltage circuits must be treated with the utmost respect, and a 500V cap is recommended for C1 unless you know that you will never use it on a valve transmitter or receiver circuit.

Here's The Simple RF Probe Source

Sound Pressure Level Meter

noreply@blogger.com (Go2Media) — Thu, 10 Jul 2008 19:35:00 +0000

This electronic circuit project is to setup home-cinema set adjusting all the loudspeaker outputs to the same level when heard from the listening position.

In practice this device is a simple (though linear and precise) ac millivoltmeter, using an existing multimeter set to 50 or 100µA fsd with the probes connected to J1 and J2 to read the results.

The precision of the measure is entirely depending on the frequency response of the microphone used but, fortunately, for the main purpose of this circuit an absolutely flat response is not required. Therefore, a cheap miniature electret microphone can be used.

Parts List:

R1 - 10K 1/4W Resistor
R2,R3 - 22K 1/4W Resistors
R4 - 100K 1/4W Resistor
R5 - 100R 1/4W Resistor
C1 - 1µF 63V Polyester or Electrolytic Capacitor
C2 - 100µF 25V Electrolytic Capacitor
C3 - 220µF 25V Electrolytic Capacitor
D1-D4 - BAT46 100V 150mA Schottky-barrier Diodes
IC1 - CA3140 Op-Amp IC
MIC - Miniature electret microphone (See Notes)
J1,J2 - 4mm Output sockets
SW1 - SPST Toggle or Slider Switch
B1 - 9V PP3 Battery
Clip for PP3 Battery

The amplifiers driving the loudspeakers must be fed, one at a time, with a sine wave in the 400Hz - 1KHz range, but different values can also be chosen. For this purpose you can use a simple signal generator circuit like one of those available on this site, namely: 1KHz Sine wave Generator or, better still, Spot-frequency Sine wave Generator.

As an alternative, the input sine wave can be provided by a CD test track, a cassette-tape or a personal computer. Please be careful and set the volume control very low, to avoid loudspeakers' damage. Switch-on the Sound Pressure Level Meter and increase the volume of the amplifier in order to obtain an approximate center-scale reading. Repeat the same steps with all channels.

Source

ESR and Low Ohms Meter

noreply@blogger.com (Go2Media) — Thu, 10 Jul 2008 16:53:00 +0000

If you repair switch-mode power supplies, TV receivers, computer monitors, vintage radios, or similar equipment, and/or if you need to measure very low values of resistance, this project can save you lots of time and aggravation - as it has for me. It measures an aspect of electrolytic capacitor performance which is very important, but normally very difficult to check: the equivalent series resistance, or ‘ESR’.

Micro-based ESR meter
Necessity is supposed to be ‘the mother of invention’, but desperation works even better and I designed this ESR meter from scratch. It’s based on a versatile Zilog Z86E0408 or Z86E0412
microcontroller - which already has two voltage comparators and two flexible counter/timers built in, greatly simplifying the rest of the circuit. A micro also allows the easy incorporation of some ‘user-friendly’ features...

This instrument has three ESR ranges, with full-scale readings to 0.99Ω, 9.9Ω and 99Ω respectively. The range is automatically selected by the micro, so your hands are free to hold the test leads. The accuracy of the prototypes was better than +/-5% of displaying reading, +/-1
digit. A single ‘-’ on the left-hand display indicates a reading above 99Ω. The readout is on two 0.5’’ (13mm) seven-segment LED displays, plus two 3mm decimal point LEDs which are
needed because the display decimal points are on the wrong side for this application.

If you forget to turn the power off, the micro will do it for you when the displayed reading has remained the same for two minutes. This feature can be disabled for uninterrupted operation from a 9V optional plugpack.

When the battery voltage is nearly too low for the circuit’s 5V regulator to function correctly, the Z86 reduces the power to the LED displays and flashes a ‘b’ on the right-hand one in the ‘offscale’ condition, to warn you to look for a new battery. (ESR Meter Manual)

Source

Audio Level Meter Circuit LM3915

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 18:37:00 +0000

This VU Meter circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display.

LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB. (datasheet)

Source

Audio Test Equipment - Pink Noise Generator

noreply@blogger.com (Go2Media) — Sun, 06 Jul 2008 03:18:00 +0000

This audio test equipment is for audio testing, a pink noise source is an invaluable tool. It is essentially a flat frequency response noise source, and will quickly show any anomolies in speaker systems, room acoustics and crossover networks.

White noise (the sound you hear when a TV is tuned to a non-existent station) has a frequency characteristic which raises the power level by 3dB with each increasing octave, and is not suitable for response testing (and will probably blow your tweeters as well). By combining a 3dB / octave filter and a white noise source, we can get a very good approximation to "perfect" pink noise, where the power in the octave (for example) 40 to 80Hz is exactly the same as in the octave 10kHz to 20kHz.

Figure 1 shows the circuit diagram for the filter, which uses the 1458 dual op-amp for economy. There is no point using a low-noise device in something which is specifically designed to make noise, so this op-amp is fine for the purpose.

Figure 1 - Pink Noise Generator Circuit Diagram

The BC548 transistor is connected so its emitter-base junction is reverse biased, which creates a nice noisy zener diode. With the values shown, the average noise output is about 30mV (broadband). The transistor zener voltage is a bit iffy, mine runs at about 9V, but it could be anywhere from 5V up to 10V. In some cases, you may find that the transistor is not noisy enough, so try a few until you get one that makes lots of noise.

The first op-amp stage acts as an amplifier / buffer, providing a very high input impedance (so as not to load the noise source), and having a gain of 11 (20.8dB). The DC voltage at the output of the buffer should be the same (or very close to) that at the transistor zener.

The positive battery supply connects to pin 8 of the op-amp, and the negative to pin 4 - don't mix up the battery polarity, or the op-amp will die.

The 10uF capacitors marked "NP" are bipolar (non polarised) electrolytics. Although film caps can be used, they will contribute nothing but cost to the final project. Non-polarised caps are needed because of an unpredictable polarity for C4 and no little or no DC across C8.

The second stage is a 3dB / octave filter, which is quite linear across the frequency band 20Hz to 20kHz. This converts the white noise into pink noise, having equal energy in all 10 octaves of the audio band.

Because of the comparatively high zener voltage of the transistor, the supply voltage needs to be somewhat higher - 2 standard size 9V alkaline batteries in series (18V) should run the unit for far longer than you will ever want to listen to it. Because of the limited capacity of the 9V batteries, no indicator LED has been included, as this would draw more current than the rest of the circuit. The power switch must be a Double Pole, Single Throw (DPST) type, as both batteries must be disconnected. The centre-tap of the batteries is the earth (or ground) for the unit. All earth points (the upside down triangles) must be connected together.

The entire circuit can be laid out on a piece of prototype board, and mounted in a suitable plastic or metal box. No special precautions are needed, other than ensuring that polarised components (transistor, op-amp, and electrolytic capacitors) are connected the right way 'round. Values of components are not critical, so standard tolerance components should be fine throughout. The use of 1% metal film resistors to keep noise to a minimum is not required in this circuit! The transistor can actually be any small signal type you have handy, and so can the dual opamp (or a pair of single opamps can be used - note that their pinouts are completely different).

If you have an oscilloscope or can get access to one, check that the noise output is not clipping (you won't be able to hear it, but if it clips, the energy spectrum will be modified). There is no easy way to check without a 'scope, and the noise output from transistors used in this way tends to vary somewhat. If clipping is observed (or you suspect it), increase the value of R3 or R4 (both 10k). Doubling the value (of one or the other - not both) will reduce the output by half. There are digital "pseudeo-random" noise generators available, but I don't like them, since they have a cycle which eventually repeats and this is very audible. By contrast, the unit described is completely random, as only analogue can be.

Figure 2 - Frequency Response of Filter

Figure 2 shows the 3dB/ Octave response obtained. It is not perfect (I have never seen one that was), but it is more than close enough for all but the most exacting of requirements. The low bass rolloff is created by the output cap and C7 (it is actually slightly greater than shown). The error is typically less than 1dB over the audio band.
Using A Noise Generator

Connect the generator to your preamp, and slowly advance the level control until the sound level is at about the level of normal speech (about 65dB). Carefully listen for any "tonality" in the sound, such as a low hum, or a point where the signal seems to disappear (sometimes referred to as a "suckout"), or anything which does not sound like pure noise. This will probably take a little practice - if you have a graphic equaliser handy, this is a great way to introduce peaks and dips to hear what they sound like.

Try listening through a good set of headphones, and compare the result with the speakers and room acoustics, you might be surprised at the result. I once read a story where an engineer was trying to find out where the hum in his noise generator was coming from. It turned out that the noise generator had no hum at all, but he was hearing the bass resonance from a badly designed loudspeaker - you can get results from these little guys!

Source: Rod Elliott - ESP

Electronic Distance Meter

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 15:45:00 +0000

This electronic circuit project is to measure distance while riding bicycle. Direct display in meter unit. Detection of rolling is made by proximity effect, when the magnet close to the reed switch. This close/open reed switch contact can use to make on-off signal. I chose MCU from Motorola, a 16-pin 68HC908QY4 for counting the pulse signal produced by reed switch.

The MCU uses internal oscillator, internal reset, so we need only to supply the +VDD and VSS. I put the decoupling cap 0.1uF to VDD and VSS. Interface signals for LCD are D4-D7, RS and E. It was 4-bit interfacing, no BUSY checking. The LCD connector is 16-pin SIP socket. D0-D3 is not used, so we must tie to GND. Also R/W# was tied to GND. Since we can not check BUSY bit, so the delay routine must be used to wait LCD ready for command and data writing. The sensor inputs are PTA2 for reed switch contact and PTA0 for 0/+5V analog input. I used small phone jack for both sensors. The analog input is optional. I haven't got the idea what sensor should be used. The power supply is battery with simple +5.1V zener diode. You can use +9V battery or 1.5Vx3 AA battery. The circuit can run properly when the supply down to +3V. Care should be taken if you will use ADC, since the VREF is the same as VDD!

Reed Switch Sensor
Figures below show a sample sensor and cable making. Later we need shrinkage tube to protect the sensor. The position when sensor when fix to the bicycle wheel also important. We need the magnetic flux perpendicular to the contact.

Download Documentation

schematic: schematic.pdf
firmware source code: LCD.C
record: lcd.s19
orcad files (schematic, layout): N/A

Source

Exclusive 2.5 GHz Frequency Counter

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 14:53:00 +0000

A frequency counter is one of the most important measuring tool we need as homebrew's of RF electronic. This frequency counter has very high performance and still is very easy to build and to use. Anyone can build it and have a professional frequency measuring tool.

The counter is based around a LCD display with 2 lines and 16 chars. I have used a HD44780 based display which is very common. A PIC16F870 circuit controls all counting and display functions. A prescaler is added to make it possible to measure up to 2.5 GHz with high sensitivity.

Download : PCB Source Code Windows Software Assembly Manual CAD PCB Program

Calculating PLL Registers in LMX2322 LMX2322 Datasheet

Source

Simple 2.5 GHz Frequency Counter

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 14:46:00 +0000

The 2.5Ghz frequency counter project is very simple but has a great use. High frequencies are more important for radio amateur who are dealing with radio transmitters and receivers. This frequency counter have ability to subtract the incoming frequency by offset(10.7MHz or 455kHz), so Intermediate Frequency of oscillator could be seen.

As this frequency counter is built under PIC16F870, it can’t measure high frequencies directly especially with high accuracy. Frequency is captured via frequency divider LMX2322 which divides by 64. Frequency counter has optional RS232 output what enables to output frequency value to PC screen or other devices. You can download all project files necessary from original page including two firmware versions 999MHz with 1kHz step and 2.5GHz with 10kHz step.

Infrared Remote Control Tester

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 03:12:00 +0000

This is a fairly easy circuit that can be used to test TV and VCR remote controls. The infrared detector module (GP1U52X) (Radio Shack 276-137) produces a 5 volt TTL pulse train corresponding to the digital code of the particular remote control key pressed. In the lower circuit, the module output is normally low with no signal received and becomes a positive going pulse train when a signal is present.

Other detector modules are available that have an inverted output as shown in the upper drawing which is the type I used, but I don't have the part number, I believe it was removed from a VCR. The pulse sequence represents the digital code of the particular key pressed along with possible manufacturer information. As the pulse train occurs, the 4.7uF capacitor is charged to about 3 volts and the capacitor voltage minus a diode drop appears across the 470 ohm resistor yielding a collector current from the 2N3904 or 2N3906 of about 5 milliamps. The collector current of the first stage flows into the base of the output transistor (MJE34 or 2N3053) which delivers around 250 mA into the indicator lamps. When the pulse train ends, the capacitor slowly discharges through the base of the first stage transistor allowing the Xmas tree lights to remain on for a about 1 second. The little Xmas lamps will operate over a wide voltage range, so you can use bulbs from almost any string, but bulbs from shorter strings (35 or less) will probably last longer operated at 5 volts.

The circuit can be powered from a small 9-12 volt DC, 250 mA or greater wall transformer. It may also need an additional 1000 uF filter capacitor across the DC output if the wall transformer does not have a built in capacitor. For use with a 9 volt battery, the incandescent lamps can be replaced with a regular LED and 680 ohm resistor and the output transistors can be replaced with small signal transistors (2N3904 or 2N3906). The total current drain will be about 25 mA with the LED lit, and 15 mA standby when the LED is off.

Source

In Circuit Transistor Checker

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 09:19:00 +0000

This simple circuit has helped me out on many occasions. It is able to check transistors, in the circuit, down to 40 ohms across the collector-base or base-emitter junctions. It can also check the output power transistors on amplifier circuits.

Circuit operation is as follows. The 555 timer ( IC1 ) is set up as a 12hz multi vibrator. The output on pin 3 drives the 4027 flip-flop ( IC2). This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LED's are arranged so that when the polarity across the circuit is one way only one LED will light and when the polarity reverses the other LED will light, therefore when no transistor is connected to the tester the LED's will alternately flash.

The IC2 outputs are also connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will turn on and produce a short across the LED pair. If a good NPN transistor is connected then LED1 will flash by itself and if a good PNP transistor is connected then LED2 will flash by itself. If the transistor is open both LED's will flash and if the transistor is shorted then neither LED will flash.

Source: Randy Linscott

Plant Moisture Meter

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 09:17:00 +0000

Stick the metal probes into a freshly watered plant and adjust R5 for a mid-scale meter deflection. The meter will monitor the soil wetness and the meter will indicate whether it is to moist or to dry. This circuit uses a dual power supply which could be created by two 9 volt batteries.

Source: Randy Linscott

Audible Logic Probe

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 09:12:00 +0000

When testing circuits with a logic probe, it is sometimes difficult to watch the LEDS on the probe to determine the logic state. With this probe the logic states are audible.

This probe is designed for TTL circuits only but could be modified for CMOS. The way it works is as follows. The 5 volt power source will be the circuit under test. Clip the ground input of the probe to the ground of the circuit being tested. The other input lead is used to probe the different chips of the circuit being tested. Any input greater then 2 volts will be high and output a high tone through the speaker. Any input less then .8 volts will be low and produce a low tone through the speaker.

Source: Randy Linscott

Audio VU Stereo Meter

noreply@blogger.com (Go2Media) — Sat, 28 Jun 2008 16:34:00 +0000

This project will indicate the volume level of the audio going to your speakers by lighting up LEDS. The LEDS can be any color so mix them up and really make it look good. The input of the circuit is connected to the speaker output of your audio amplifier.

You want to build two identical units to indicate both right and left channels. The input signal level is adjusted by the 10k ohm VR. If you wish to make a very large scale model of this unit and hang it on your wall there is an optional output transistor that can drive many LEDS at once. The unit I built drove three LEDS for each output. The sequence of the LEDS lighting are as follows Pin 1, 18, 17, 16, 15, 14, 13, 12, 11, 10.

Source: Copyright 1998 Randy Linscott

Milligauss Meter Circuit

noreply@blogger.com (Go2Media) — Sat, 28 Jun 2008 15:56:00 +0000

The circuit provides an easy yet reliable way to detect the intensity of a.c. (or e.l.f.) fields around the home or workplace. It is doubly effective because it does not merely detect the electromagnetic radiation emitted by electrical appliances, but the electromagnetic energy actually absorbed by the body.

The circuit in is a standard charge pump which is charged by the alternating eddy currents induced in the human body by a.c. fields. C1 charges virtually instantly, and is read by a digital (or high impedance) voltmeter.

To obtain a very rough translation from millivolts to milligauss (the unit of magnetic field strength), divide the millivolts reading by four. For example, 1000mV will yield 250 milligauss.
A rough guide to the readings follows:

Up to 3 milligauss - Low electromagnetic radiation
25 milligauss - Significant electromagnetic radiation
100 milligauss - High electromagnetic radiation
250 milligauss - Maximum risk exposure

Detrimental effects have been reported at doses as low as 3 milligauss, and a series of studies since the 1970's has shown that sustained exposure to high e.l.f. doses heightens the risk of certain cancers and miscarriage.
Readings are taken while holding the probe in one hand. The closest proximity to the electromagnetic source does not necessarily give the highest reading, probably because the induced currents in the body remain localised at close proximity.

The Sensor
Is any piece of metal (e.g. a short stub of copper piping, even a short piece of fencing wire) that makes good contact with the hand.

Partlist
1 x 47n capcitor (C1)
1 x 200p capcitor (C2)
2 x 1N4148 diodes (D1, D2)
1 x High impendance voltmeter
1 x sensor (see description)

Copyright Rev. Thomas Scarborough
[Contact the author of this article at scarboro@iafrica.com]

UTP Cable Tester 2

noreply@blogger.com (Go2Media) — Sat, 28 Jun 2008 15:34:00 +0000

The UTP Cable Tester can be used for many purposes. Mainly to test a UTP network cables of course. However it can also be used to find the right cable in a large bundle of identical looking cables. In fact the circuit can be used or adapted to test any type of cable of any number of wires, provided that the tester is equipped with the appropriate connectors.

The UTP Cable Tester consists of 2 tiny boxes that have to be connected to each end of the cable under test. One of the boxes contains a signal generator, powered by a standard 9V battery. The other box contains 8 LEDs that indicate the cable's condition.

The principle of operation is very simple: A good cable will show a single walking light. However when the lights are lit out of order you'll know that some wires have been switched in one or both of the connectors. If one or more lights don't light you'll know that one or more wires are cut. If two or more lights light up simultaneously you'll know that two or more wires are shorted together.

The Signal Box
The Signal Box is powered by a 9V battery B1 which can be switched on and off by switch S1. Diode D2 protects the circuit in case the battery is connected the wrong way up. Current drain is minimal, approximately 5mA, which ensures quite a long battery life.

The IC 4060 generates a low frequency at its output. The exact frequency is not that important, as long as you can identify signals in the wrong order on the Display box. I choose a frequency of about 3Hz, resulting in a total loop time of approximately 3 seconds. You may change the frequency by changing the value of C1 to suit your own needs.

This low frequency is fed to the input of the IC 4017, which is a decade counter. It has 10 outputs, only one of which will be high at any time. Every time the counter receives a low to high transition it advances to set the next output high. It has 10 stages, and we need only 8 LEDs on the Display Box. One of the remaining stages is used to flash a LED on the Signal Box to indicate that it is functioning. The 10th stage is obsolete, and no LEDs will be on during that time. This way a short pause is introduced on the light pattern on the Display Box.

If you want you can use the 10th output to test the shield of an STP cable. In that case you'll need an extra resistor, LED and diode in the Display Box. The resistors on the outputs must limit the current flow and still leave some voltage to drive the affected LEDs in case 2 wires are shorted.

I could have used a programmable controller like a PIC16F84 or AT89C1051. The program would be quite simple. I deliberately chose the discrete approach though for a few important reasons:

* It is cheaper than a micro controller.
* It consumes less supply current.
* It does not require a programmed device, making it easier for all of us to build.
* It does not require a regulated voltage, making the power supply very simple.

But if you are only a little familiar with micro controllers, feel free to program the Signal Box in a processor of your choice.

The Display Box
The Display Box contains 3 RJ-45 connectors. The first connector, marked 1:1, is used to test Patch cables. On the second connector, marked Xll, the wires 1 & 2 are crossed with the wires 3 & 6. It is used to test normal Cross cables for 10baseT and 100baseTX networks. The third connector, marked XX, is used to test 100baseT4 cables, which have all 4 pairs of wires crossed.

The circuit can be divided into 8 identical parts which all contain an LED, a normal diode and a resistor. The anodes of all diodes are connected together creating a virtual ground. Remember that only one output of the 4017 was high, all other outputs are low at that time so there will always be enough sinking capacity for the LED current. The LEDs are connected to the RJ-45 connectors in a row. Pin one to D18, pin 2 to D17, etc. This order is very important for it will determine the walking behaviour of the light during testing. The resistors are used to limit the current through the LEDs to about 4mA, which is enough for modern LEDs.

I deliberately didn't use just one resistor for the whole circuit. In normal conditions it wouldn't be a problem if I did. But when 2 wires are shorted 2 LEDs would have to share their current by this one resistor, creating a higher voltage drop reducing the current through the LEDs even further.

Parts List
B1 9V Battery
S1 Any kind of on/off switch
C1 10nF
C2 Elco 47uF / 16V
R1 56 kΩ
R2 1 MΩ
R3 1.8 kΩ
R4..R11 8 times 470 Ω
D1 LED of your choice
D2 1N4148
4060 (any manufacturer will do)
4017 (any manufacturer will do)
4 RJ-45 connectors

D11..D18 8 LEDs of your choice
D19..D26 8 times 1N4148
R12..R19 8 times 1.2k Ohm

Practical examples

This first example shows the pattern for a good cable. All wires are connected, none are shorted, none are mixed.

LED 3 doesn't light in this example, which means that wire 3 is cut.

In this example we can see that the LEDs 3 and 5 light out of order. LED 5 lights, when LED 3 should, and LED 3 lights when LED 5 should. This indicates that the wires 3 and 5 are mixed.

This final example shows that the LEDs 3 and 5 light together, indicating a short between the wires 3 and 5. Notice that both LEDs light up twice. Once if only LED 3 should light, and once when only LED 5 should light. In reality both LEDs will light with lower intensity than normal because the voltage coming from the IC is halved.

If an error is indicated by the UTP Cable Tester, it may be a bit tricky to find the faulty wire(s) on Cross cables. The wire number indicated by the LEDs are the wires seen from the connector at the Display Box's end. Testing the other way around can show other wires being faulty! This is normal behaviour though, and is the nature of Cross Cables. (source)

A Simple UTP Cable Tester

noreply@blogger.com (Go2Media) — Sat, 28 Jun 2008 14:51:00 +0000

The circuit below is designed so that when the ends of a UTP cable are plugged into each of the "RJ45 Sockets", the circuit for each pair is completed and the LEDs light up. If there is a break in a wire (or the leads are incorrectly terminated) the corresponding LED will not light. For remote testing (where you can't get at both ends) cut the board apart and plug the "terminator" section into one end and the "Tester" end into the other.

How it Works
The wires in CAT 5 Unshielded Twisted Pair (UTP 8-wire) are arranged in pairs. (Pin1/Pin2, Pin3/Pin6, Pin5/Pin4, Pin7/Pin8).

Note
This circuit will not indicate if the wires in a pair are crossed over. I haven't tried it yet, but it should be possible to modify the circuit and use 'Bi-polar' Red/Green LEDs instead of conventional LEDs to indicate 'crossed' wires. more

Microwave SWR Meter

noreply@blogger.com (Go2Media) — Tue, 17 Jun 2008 06:09:00 +0000

Basically it consists of 2 pieces of UT141 semi rigid coax. On both pieces of semi rigid coax, a slot of around 30mm in length is filed to expose the centre conductor. The slot width is about 2mm. The two slots, one on each coaxial cable are then put together, such that the transmission lines are parallel, and soldered along the full length on both sides. Make an effort to solder properly. The 30mm window in each piece of semi-rigid must be lined up so the coupling will be efficient.

This technique not only provides good coupling, but ensures that both transmission lines have a relativly constant 50 ohm impedance.

The main through RF line is terminated with good quality N type chassis sockets, whilst the coupling line has SMA plugs attached to it.

The coupling line is then terminated with 50 Ohm loads, made with two 100 ohm surface mounted resistors. These resistors are mounted on the back of an SMA socket (see circuit diagram below).The centre pin of the SMA socket also has a mixer diode from an old Marconi LNB connected to it. Ideally, a good quality microwave diode would be used instead of the mixer diode from the LNB. The other pins of the mixer are supported on 1n and 10K chip components, with the DC output being taken from the top of each 10K resistor.

The picture below shows the SMA circuitry in a little more detail. In addition to the detector circuit, a simple op-amp voltage amplifier circuit is required as the output from the mixer-diode-detectors are small. A switch and pot are required to select forward or reverse voltage. Once the meter is calibrated using the pot for full scale reading on forward power, then reverse readings can be taken with relative ease.

Using this SWR meter for 2.4Ghz wireless lan antenna testing is simple, and providing UHF construction techniques are observed, this meter will perform very well.

A simple but effective SWR meter for the low microwave bands.
Written by: G4RFR ( FRARS )
Source: http://www.frars.org.uk/cgi-bin/render.pl?pageid=1085#
Thank

Power and SWR Meter

noreply@blogger.com (Go2Media) — Tue, 17 Jun 2008 05:55:00 +0000

The Power and SWR Meter kit, is a handy accessory for both station and field use, designed by Steve "Melt Solder" Weber KD1JV. It is a self contained power meter and SWR indicator for 50 Ohm coaxial transmission lines.

With this device, you can measure the output power of your QRP transmitter and the SWR on the transmission line to your antenna. Frequency coverage is all amateur bands from 160 to 6 meters.

The circuit uses bright LED's to display the power and SWR in binary coded format. This results in a very compact test instrument.

The SWR/Power meter is powered by two internal "AAA" battery cells. The meter automatically powers itself down after a period of inactivity to conserve battery life.

Specifications:

160 to 6 meter operating range
9.9 Watt and 990 mW power scales
Peak hold mode ( 9.9 watt scale only)
1:1 to 9.9:1 VSWR scale
Accuracy 5% of reading
Sensitivity, 20 mw minimum
Manual and auto power shut off
Self contained, fits in Altoids tin
Two digit BCD encoded display
Single push button operation
Powered by 2 "AAA" batteries
Ideal for portable and field use

Download Power/SWR Meter Manual

What you get: You will receive the PC board, all board mounted parts and the instruction/operation manual. The builder will need to provide the enclosure, antenna connectors of your choice and the batteries.

Source: http://4sqrp.com/kits/swr_pwr/swr_pwr.htm

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noreply@blogger.com (Go2Media) — Tue, 10 Jun 2008 11:51:00 +0000

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