Test Equipment and Measurement

Capacitance Meter

2009-06-29T05:20:00.000-07:00

This Capacitance Meter project is more complex than the others described earlier. However, when finished, you will have an instrument capable of measuring all but the largest capacitors used in radio circuits. Unlike variable resistors, most variable capacitors are not marked with their values. As well, the markings of capacitors from salvaged equipment often rub off. By being able to measure these unmarked components, this project will prove useful to the constructor, vintage radio enthusiast or antenna experimenter.

Position Range Use X10 switch to measure up 10uf.

Use X0.5 switch for better readings on low values.

a = 1 uf

b = 100 nf

c = 10 nf

d = 1 nf

e = 100 pf

The common 555 timer IC forms the heart of the circuit. Its function is to charge the unknown capacitor (Cx) to a fixed voltage. The capacitor is then discharged into the meter circuit. The meter measures the current being drawn through the 47 ohm resistor. The 555 repeats the process several times a second, so that the meter needle remains steady.

The deflection on the meter is directly proportional to the value of the unknown capacitor. This means that the scale is linear, like the voltage and current ranges on an analogue multimeter.

The capacitance meter has five ranges, from 100pF to 1uF, selected by a five position two pole switch. In addition, there is a x10 switch for measuring higher values and a divide-by-two facility to allow a better indication on the meter where the capacitor being measured is just above 100, 1000pF, 0.01, 0.1 or 1 uF.

Component values are critical. For best accuracy, it is desirable that the nine resistors wired to the Range switch have a 2% tolerance. If 0A47 diodes are not available, try OA91 or OA95 germanium diodes instead. Construct the meter in a plastic box; one that is about the size of your multimeter but deeper is ideal. The meter movement should as large as your budget allows; you will be using it to indicate exact values. A round 70mm-diameter movement salvaged from a piece of electronic equipment was used in the prototype. The meter you buy will have a scale of 0 to 50 microamps. This scale needs to be converted to read 0 to 100 (ie 20, 40, 60, 80, 100 instead of 10, 20, 30, 40, 50). Use of white correction fluid or small pieces of paper will help here.

The components can be mounted on a piece of matrix board or printed circuit board. Use a socket for the IC should replacement ever be needed. Keep wires short to minimise stray capacitance; stray capacitance reduces accuracy.

Calibrating the completed meter can be done in conjunction with a ready-built capacitance meter. Failing this, a selection of capacitors of known value, as measured on a laboratory meter, could be used. If neither of these options are available, simply buy several capacitors of the same value and use the one which is nearest the average as your standard reference. Use several standards to verify accuracy on all ranges.

To calibrate, disable both the x10 and divide-by-two functions (ie both switches open). Then connect one of your reference capacitors and switch to an appropriate range. Vary the setting of the 47k trimpot until the meter is reading the exact value of the capacitor. Then switch in the divide-by-two function. This should change the reading on the meter. Adjust the 10k trimpot so that the needle shows exactly twice the original reading. For example, if you used a 0.01 uF reference, and the meter read 10 on the 0.1 uF range, it should now read 20. Now switch out the divide-by-two function.

If you are not doing so already, change to a reference with a value equal to one of the ranges (eg 1000pF, 0.01uF, 0.1uF etc). Switch to the range equal to that value (ie the meter reads full-scale (100) when that capacitor is being measured. Switching in the x10 function should cause the meter indication to drop significantly. Adjust the 470 ohm trimpot so that the meter reads 10. Move down one range (eg from 0.01uF to 1000pF). The meter should read 100 again. If it does not, vary the 470 ohm trimpot until it does. That completes the calibration of the capacitance meter. Now try measuring other components to confirm that the measurements are reasonable.

With care, an accuracy of five percent or better should be possible on most ranges.

Source: Capacitance Meter

Transistorized Dip Meter

2009-06-28T22:33:00.000-07:00

This dip meters use 2SC2369 transistor for RF Oscillator and 2SC458 for AM Tone Oscillator. VR 10 K potentiometer is a linear type it adjust the working voltage of the RF oscillator part from 0~9 Volt DC, it influence the meter reading sensitivity and in the instance the RF power. This Dip meter is a multi-function; it can also be used as a field strength meter and or AM transmission monitor when a headphone replaces the meter. Beside it can be used as a RF signal generator for receiver tuning purpose.

2 ganged air type variable capacitor normally use in FM Receiver is used for frequency tuning. The meter full scale reading is 100 µA, using a larger scale will need an extra DC amplifier to allow a full-scale meter setting.

The tone oscillator is a capacitive resistive feedback type that generate an audio tone of ± 1000 Hz. with a capability of modulating the RF oscillator for ± 30% modelation depth.

Source: Transistorized Dip Meter

RF Wave Absortion Meter for 1 to 950 MHz

2009-06-25T02:42:00.000-07:00

This RF Wave Absorbion meter will detect signals between 10cms and 10m away all acording to the setting of the 22MegOhm gain adjustment potentialometer and the power of the transmitter. The RF signal is detected across the germamium OA91 doides and rectified to a d.c. level driving a 10LED driver IC. The LED's are marked 1 to 10 indicating the strength of the detected RF signal.

This circuit is ideal for tuning up low power transmitters or locating hidden transmitters. If a specific frequency band is required, replace the OA91 diode that goes to negative with a parrallel tuned circuit as indicated. For 27MHz L=10Turns and C=39PF, for 50MHz L=7turns and C=27pF, for 80MHz L=5turns and C=12pF, for 110MHz L=4turns and C=10pF, for 150MHz L=3turns and C=8.2pF and for 180MHz L=2Turns and C=2.2pF. All coils are 22SWG wound on a 10mm air former.

Source: 1 MHz to 950 MHz RF Wave Absortion Meter With LED Signal Indication

LED RF Signal Meter

2009-06-25T02:30:00.000-07:00

This is a high quality RF signal meter based around the Analog Devices AD8313 0.1 GHz - 2.5 GHz logarithmic detector IC. It is capable of detecting signals as low as -80 dBm. When combined with 2.4 GHz or 915 MHz bandpass filters, it makes a quick visual reference to the amount of noise in the ISM bands in that particular location.

It also makes a handy visual tool for verifying that your antenna is indeed radiating energy.

Source: LED RF Signal Meter

Basic Multimeter

2009-06-25T02:13:00.000-07:00

A number of shunts and multipliers selected by a switch can be used in association with a single basic meter to form a multirange instrument, known as a multimeter. this is capable of measuring volts, current and resistance.

A multirange meter can be constructed in two units, the first containing the 0-1mA meter movement with switches to select various shunt and series resistors to give six d.c. current ranges up to 1 amp and eight d.c. voltage ranges up to 1000 volts. An internal battery provides an ohms range readable up to 200,000 ohms which corresponds with the first division of the meter (0.02mA)

An Add-on unit contains a meter rectifier with associated switched series resistors to give four a.c. voltage ranges up to 100 volts while additional shunt and series resistors (Ra and Rb) extend the range to 10A and 5Kv. When using the add-on unit the main instument is set to measure 1mA FSD and the add-on unit is connected to its terminals by its lugs.

The series resistors are 1% tolerance high stability types while the shunts are made of lengths of Eureka resistance wire. The wire used on electric fire elements is ideal for the lower value shunts. The values have been calculated for a meter resistance of 60 ohms internal resistance but would need modifying for other values. In any case, the precise value of each shunt should be adjusted experimentally to give the correct reading against a meter of known accuracy.

To calculate Rb: Rb= 1000V/I

Where I is the FSD of the meter and V is the desired voltage range

To calculate Ra: Rs= Rm/n-1

Where Rm is the meter resistance and n is the scale multiplication factor.

For example: If a milliammeter of 10 ohms resistance and a FSD of 1mA is to be used to measure 100mA, a shunt must be provided to carry the excess current, that is 100-1 milliamps,i.e 99mA. Thus the required shunt resistance is:

Rs= 10/100-1 = 10/99 = 0.101 ohms

Source: Basic Multimeter

Grid DIP Meter

2009-06-25T02:03:00.000-07:00

This circuit was developed by Luigi Falcone, I1FLC. He uses seven plug in coils covering 3.0 to 30Mhz in a Colpitts oscillator circuit. The coaxial socket J2 permits connection to a frequency meter when required. The coils are wound on Teflon formers with two "female" sockets which plug-in to two "male" sockets on the instrument. TR2 forms a DC amplifier permitting the use of a 1mA FSD meter with sensitivity controlled by R7. With TR1 switched off (via S2) the instument forms a field strength meter/RF sniffer.

It is important that the oscillator components are mounted rigidly and not subject to "hand capacitance effects" in use.

If a somewhat larger value variable capacitor was used with a slow motion drive the number of coils to tune 3 to 30 Mhz could be reduced.

Source: Grid DIP Oscillator (GDO)

Diode RF Probe

2009-06-25T01:52:00.000-07:00

This RF probe allows RF to be measured in the presence of d.c. The germanium diode should be tested for high reverse resistance, otherwise misleading results may be obtained. The 100pf capacitor should be capable of withstanding the highest dc voltage which is likely to be met. The 1M ohm and 0.001uF capacitor act as a low pass filter to prevent RF entering the Digital Voltmeter.

An alternative circuit is shown below, again the probe should be in a screened enclosure and the connection to the DVM should be screened lead.

Source: RF Probe

Sound Level Meter with LM3915

2009-01-03T05:52:00.000-08:00

Here's a nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This audio meter circuit can also be integrated into audio amp projects.

Note:

V+ can be anywhere from 3V to 20V.
The input is designed for standard audio line voltage (1V P-P) and has a maximum input voltage of 1.3V.
Pin 9 can be disconnected from +V to make the circuit use a moving dot display instead of a bar graph display.

Source: Sound Level Meter

Continue reading : R-2R Digital to Analog Converter

Program for Drawing Analog Meter Scales

2009-01-02T10:24:00.000-08:00

A Windows® meterscale drawing program to allow you to design and print professional-quality meter scales on your printer. Nice options include the ability to import a graphic (and resize and place it where you want), make a modern-looking "flattened" scale, use seriff or sans-serif fonts of any size and specify the scale colors.

This meter scale drawing program is designed to have a computer do the hard work in making a precision scale for a d'Arsonval analog meter. The resulting scales will typically be nicer-looking than those found on many commercial meters. Here are the highlights of this Windows program:

This program has the uncommon ability to "flatten" the arc a user-selectable amount to make a more modern-appearing scale. This is most usable with the thin "tubular" or "spadeless" style of pointer.
The program does dB, vu, VSWR and S-meter scales. Each of those routines has appropriate options for customization.
A graphic may be imported and placed on the scale. All the common graphic types (.BMP, .GIF, .ICO and .JPG) are accepted. Width, height and placement can be freely specified.
Meter draws up to four scales on a meter face, etc.

Download Program for Drawing Analog Meter Scales, the latest version (2.30)-4 MB

More Detail Program for Drawing Analog Meter Scales

Continue reading: How to Improve The Fidelity of Playback-RIAA

Audio VU Meter with LM324

2009-01-02T10:20:00.000-08:00

This Audio measurement circuit uses two quad op-amps to form an eight LED audio level meter. The op-amp used in this particular circuit is the LM324. It is a popular IC and should be available from many parts stores.

The 1K resistors in the circuit are essential so that the LED's turn on at different audio levels. There is no reason why you can't change these resistors, although anything above 5K may cause some of the LED's to never switch on. This audio meter circuit is easily expandable with more op-amps, and is not limited to use with the LM324. Pretty much any op-amp will work as long as you look up the pinouts and make sure everything is properly connected.

The 33K resistor on the schematic is to keep the signal input to the circuit at a low level. It is unlikely you will find a 33K resistor, so the closest you can get should do. The value of this resistor may need to be changed, so it is best you breadboard this circuit before actually constructing it on PCB. The circuit in it's current form will accept line level inputs from sources such as the aux out on a Hi-Fi, all though could be easily modified to accept speaker inputs.

The audio + is connected to the main positive rail, while the audio - is used for signal input. The 50k pot can be used to vary the sensitivity of the circuit.

Source: Audio VU Meter

Continue reading: Improve The Fidelity of Playback-RIAA

Peak Reading Audio Level Meter

2009-01-02T10:15:00.000-08:00

With using a single Mosfet Op-amp this circuit samples the audio input and displays peak readings. Using minimum component count; this simple circuit will indicate peak audio response on an analogue meter, similar to a tape recorders meter. The circuit uses an opamp as a non inverting amplifier, but with one addition - a diode in the feedback loop. The circuit has a fast response time and slow decay time to indicate peak readings.

The 1N4148 diode provides half wave rectification of the input signal, the dc output being smoothed by the 22u capacitor. the capacitor will charge to the peak value of the input waveform, and then discharge via the meter and 18k resistor. I used a meter with a FSD of 150uA, but any meter with a FSD in the range 50-250uA may be used. The discharge time is around a quarter of a second. Increase the 22uF cap for a longer discharge time, or omit altogether to make an instantaneous reading level meter.

This audio level meter circuit will only work with a MOSFET type opamp, bipolar types i.e. 741 and J-FET opamps such as LF351 will not work in this circuit.

Source: Peak Reading Audio Level Meter

Continue reading: How to Improve The Fidelity of Playback-RIAA

Audio Level Meter

2009-01-02T09:56:00.000-08:00

This is audio meter that can be monitored using a small panel meter with this circuit built from discrete components. The audio level meter circuit has a flat frequency response from about 20Hz to well over 50Khz. Input sensitivity is 100mV for a full scale deflection on a 100uA meter. Built on two common emitter amplifiers, the first stage has a preset resistor which may be adjusted for a FSD.

The last stage is biased to operate at roughly half the supply voltage for maximum ac voltage swing. Audio frequencies are passed through the 10u dc blocking capacitor and the full wave bridge rectifier converts the signal to a varying dc voltage.

Note that the meter reading is instantaneous and will not provide a "peak" reading.

Source: Audio Meter

Continue reading : Function Generator 20Hz-200KHz

An Advanced VHF Wattmeter

2008-11-23T17:37:00.000-08:00

This homebrew instrument is an RF power meter project.It presented a simple instrument for the homebrewer to measure RF power well through VHF. There are two meters and more controls that are associated with the instrument’s low-frequency signal processing or “support” circuitry.

The reference instrument incorporated a built-in analog meter and provision to connect an external DVM. It also utilized a conversion chart to relate meter readings to RF power. Both digital and analog displays built in for both an accurate, high resolution numeric power readout and a trend indicator at the same time.

Download Advanced VHF Wattmeter

Continue reading : Build Function Generator 20Hz-200KHz

NRVS RF Power Meter-Test Equipment

2008-11-21T17:02:00.000-08:00

The NRVS Power Meter is brand new product of Rohde & Schwarz for RF measurement. It's an ideal instrument for a great variety of power measurement applications in labs and systems. Thanks to its intelligent sensors with calibration data memory and thermocouple sensors - which make adjustments by the user superfluous - NRVS provides at all times high-precision measurements free of operator's errors.

Features of The NRVS RF Power Meter:
- Fast power, level and voltage measurements
- Intelligent NRV-Z probes and URV5-Z sensors: plug and play
- GPIB interface
- DC frequency input for tracking frequency-response correction
- Analog output
- Menu-guided operation with softkeys
- Storage of 20 complete instrument setups
- 13 digital filters for noise suppression, automatic or manual filter selection
- Sensor check source (optional)

Characteristics of The NRVS RF Power Meter

Display, Measurement results, units and various items of information are displayed on a large easy-to-r0ead 4-1/2-digit LCD in three selectable steps of resolution.
Pulse Power, If pulse-modulated RF signals are measured, NRVS calculates the pulse peak power from the measured average power and the entered pulse duty factor, and reads out the result directly. The use of Peak Power Sensors NRV-Z31 and -Z33 for measuring the peak envelope power (PEP) is highly recommended.
Measurement Rate, The attainable measurement rate not only depends on the type of sensor used but also on the setting of the averaging filter. NRVS automatically makes the appropriate settings by determining the optimum averaging time required for a steady readout as a function of level and selected resolution. This automatic selection can be switched off.

Download specifications of the NRVS RF Power Meter

Continue reading : Build Function Generator 20Hz-200KHz

R-2R Digital to Analog Converter

2008-11-21T00:05:00.000-08:00

Here's a cheap Digital to Analog Converter Circuit. Use this circuit as a low cost alternative to a commercial DAC. It is important that the latch be a CMOS device, so that the outputs drive to Vcc when they are high. (TTL devices only drive to 2.4 volts or so).

Why choose the '573 latch rather than the '373 which can also be used. The '573 has the advantage of sequential pin-outs for the Q0 - Q7 pins, making it easier to connect in most circuit layouts.

The LM358 OpAmp is a good choice for this circuit for two reasons: 1) It can be powered from the 5V supply. 2) Its output can go to 0V without a negative power supply. Note that the LM358 is a dual OpAmp, so the other half is unused in this circuit. Source: R-2R Digital to Analog Converter

Continue reading: Test Oscillator

How to Improve The Fidelity of Playback-RIAA

2008-11-20T23:46:00.000-08:00

This post taken from Bill's Hobby Circuit Library and He says, if your stereo amplifier does not have an input for a record player, you should use this circuit between your turntable and your amplifier. The output of your turntable follows a gain-bandwidth curve called the RIAA compensation curve. The standard AUX input on your stereo does not. Records will sound very strange without an RIAA preamp.

The RIAA compensation curve was adopted in the mid 1950s, as a way of dramatically improving the fidelity of playback. This curve takes into account the limitations of the mechanican recording system on the record surface. At low frequencies, this amplifier provides 20dB of gain. At medium frequencies it provides no gain, and at high frequencies it provides 20dB of attenuation.

Note that only two Opamp packages are used. Each type is actually a dual Opamp. The left and right amps share one amp of each type from each dual package. This circuit is also used as the example for the "Custom Etched Circuit Boards" section. In that section you will find instructions for making a custom circuit board for this preamp. If you want to make your own circuit board for this project, you can download full size artwork there as well.

Originally posted by Bill. Electronics Reference Library Home Page

Continue reading: Audio Test Oscillator

Build Function Generator 20Hz-200KHz

2008-11-12T14:20:00.000-08:00

This Function Generator built around a single 8038 waveform generator IC, this circuit produces sine, square or triangle waves from 20 Hz to 200 kHz in four switched ranges. There are both high and low level outputs which may be adjusted with the level control. This project makes a useful addition to any hobbyists workbench as well.

Source: Build Function Generator 20Hz-200KHz

Continue reading: Audio Test Oscillator

Audio Test Oscillator Design Consideration

2008-11-12T13:41:00.000-08:00

An audio oscillator has to be considered essential for anyone working in with hi-fi gear. Even better if you have access to an oscilloscope, you will be able to make proper measurements on everything from preamps, RIAA equalisation stages for vinyl disks, tone controls, crossover networks, etc.

What factor must be considerated in building a good audio test? According to Rod Elliot there are several things must be done in order to create a usable audio oscillator.

The frequency must be defined with a suitable filter, so the output will be at a known frequency
The gain must be stabilised to exactly that value which will sustain oscillation, without dying away or becoming a square wave (or just distorting)
The frequency response of the amplifier should be considerably greater than the highest frequency to be generated to ensure amplitude stability at all frequencies
Output impedance must be low enough to ensure that there is no significant loading from the input circuitry of any expected load
An output attenuator is needed so that a defined level can be preset, preferably without having to measure it before use
Ideally, a square wave output should also be provided - this is only really useful if the user has access to an oscilloscope

Wien Bridge Basic Circuit

For examples, one of types of oscillator that almost universally used for audio work is the Wien Bridge.This is chosen because of its stability, relatively low distortion and ease of tuning.

Here's a link for Audio Test Oscillator Building info.

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2008-11-11T23:46:00.000-08:00

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