Schematics of delabs

Interface a uC to PC RS232 with MAX232A

2009-10-15T07:19:00.000+05:30

This is the standard configuration on how to Interface a uC like 8051 to PC RS232 with MAX232A. The UART or Serial port was not present in 8049/8749 chips which were the ancestors of 8051/8031. Pages of code were needed to make a software UART in MCS-48. The 8051 integrated the hardware UART and short commands made it tick. The most important innovation which made uC popular was the C in 80C31. C is for CMOS. This made the chip work cooler and work on even batteries and small power...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Perpetual Candle - White LED Lamp on Ni-Cd

2009-10-08T10:45:00.000+05:30

This is a easy to build LED lamp circuit for Learning and building skills. This is the first draft schematic V 1.0. It will need improvements for Higher Power Lighting. From Schematics of delabs I will give a short summary, The LM317 here configured for around 6.4V DC. The Q3 BC547 limits the current, you can select R3 to suit, make it 1/2W. The Ni-Cd battery pack 1.2 * 4 will not get Over-Current or Over-Voltage due to this circuit. The IRF540 Mosfet or any other equivalent you have...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Resistance Measurement Analog LED Meter

2009-02-22T07:05:00.000+05:30

This is a LED Analog Meter, This can be used as a Resistance Meter and Low Impedance Voltmeter for Battery Levels. To measure battery voltage, the R5-R12-R17 etc. part of the Reference Resistor Divider Network can be modified to suit. Shown here is for 4 LEDs, Use Three LM324 for 12 or More LEDs and Cascade as shown. This cannot Measure Voltage levels from High Impedance Sources, will work for Battery Voltage Tests. To make it into a Continuity tester. R27 must be a short and R23 5 Ohms. The...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Analog Level by BCD Thumbwheel Switch

2009-02-20T11:35:00.000+05:30

BCD Thumbwheel Switch is used to input-set data in digital form, this can be read by digital circuits, uC and uP systems and PLC-SCADA Interfaces. In the early transition of analog to digital, before uP became acceptable, Digital systems without uP were made, it even had printers, RAM and displays. The uP systems were coming in, uC had not yet come and uP systems had to still win the confidence of the Prudent Industrial Design Engineer. The drawbacks of uP based systems used in Computers, in...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Opamp Supply on Buffered Virtual Ground

2009-02-19T16:01:00.000+05:30

When a Inverting Opamp Configuration is at a steady state, we say the Inverting Input is at a Virtual Ground. That means it is at 0V w.r.t to the dual power supply ground, but it cannot drive or draw any current. It is at a high impedance, but still at 0V. When you buffer this 0 V, you get a low signal ground for a opamp supply. This gnd. can sink and source in a couple of mA. You can use it with low power opamp circuits for portable battery operated devices. This creates a virtual +/- 6 V...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Voltage to Frequency Converter ICL8038

2009-02-19T13:10:00.000+05:30

This was a small circuit made for driving an Impact counter. The heart being ICL8038. It must have been a Motor driving a Conveyor, the motor has a feedback attachment called Tachogenerator. Only part of the circuit is shown here. See the image of product here Tacho Counter. The configuration is derived from the Application Notes of Intersil. The Voltage from Tachogenerator is Measured on a DPM-DVM and also fed to this circuit after attenuation and filtering. The square pulses of 8038 is...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Millivolt Source - Field Calibration Current Loop

2009-02-19T11:50:00.000+05:30

This is easy to rig millivolt source for field calibration or troubleshooting of 4-20 mA current loops. Here a Darlington pair is used for current amplification which reduces the Ib error as gain is very high. A rotary switch selects, 4-12-20 mA Preset points. A Bourns multi-turn wirewound Pot can also be used with a digital dial. Enclose in a dust proof handheld box. Read more on process calibration.

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Precision Op-Amp Current Source

2009-02-19T09:01:00.000+05:30

In this circuit we tackle the error indicated in the earlier Current Source. The LM336-2.5V eliminates the tiny error of the regulated supply and resistors. Thereby increasing Precision to a higher degree. The opamp mirrors the stable 2.5V across P3 + R13. With P3 Bourns 10 Turn Trimpot you can trim the current for calibration. Q1 BC557B having a Beta - hfe of 200 is used. But a higher gain or a FET here may reduce error further, that may be needed if you are going for 16 Bit or more...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Current Source for Resistance Measurement

2009-02-18T19:01:00.000+05:30

Here is a current source you can build for resistance measurement. When the current is held constant, you know as per Ohm's Law the Voltage across Resistor is proportional to Resistance value. The supply is +12 and -12, The total voltage across R6 + R7 is 24V. Then 24V / 120K = 0.2mA. The voltage across R6 is (10K * 0.2mA) = 2V. The same is reflected across R5 in this feedback configuration. That means Q3 is a 2V / 1K = 2mA source. If my calculations are right. There are sources of errors...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Ohmmeter - Simple Resistance Measurement

2009-02-17T15:40:00.000+05:30

Measurement of resistor values in circuit configurations are required to be made often, as these might have changed in value due to various tolerance ranges, and hence could be the cause of faults. Likewise the resistance of components used in a circuit, may need to be known. In such cases the measurement of resistance is a must. The circuit used for measurement of voltage can be modified to measure the value of the unknown resistance. The principle followed is the measurement of voltage...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Ammeter and Precision Rectifier

2009-02-16T13:02:00.000+05:30

Studying current measurement is a prerequisite for many of the measuring techniques. The current parameter mainly specifies the power consumption in a circuit, given the value of resistance. It is found convenient to measure current rather than voltage for knowing power output and determining efficiency. It may be required to measure leakages in circuits at certain times. Hence the measurement of current constitutes a priority. Measurement of DC Current - The circuit diagram for the...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Voltage to Current Source 4-20 mA

2009-02-16T11:20:00.000+05:30

The 0-1V to 4-20 mA Converter published earlier is a current sink, Here is a circuit that is a voltage to current converter but with a current source. You can use a LM358 or LM324. The first opamp is a Voltage to Current with a sink output. That current creates a varying voltage w.r.t the 12V DC supply, this varying voltage is mirrored by the second opamp across the source output resistor. This way a constant current is obtained with a sourcing output. The control elements are small signal...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Diode Reverse Bias Leakage Tester

2008-12-24T09:05:00.000+05:30

This is a Test arrangement for Leakage Testing of Diodes on Reverse Bias. The leakage current indicates the ability of the diode to withstand higher voltages. An AutoTransformer or Variac can be used to vary the test voltage. Even Plastic capacitors can be tested for leakage this way. Safety Precautions - Use a Isolation 1:1 transformer for safety. This circuit has to be enclosed in a insulated cabinet. A Jig or Acrylic Safety Plate with clamp can be used to connect the diode. The voltage is...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Voltage Doublers and Multipliers

2008-12-24T08:10:00.000+05:30

Voltage multipliers are used to obtain low current high voltage, from an existing AC Source. Step up transformers can be used, but the insulation problems and care that has to be taken for HV above 1kV, make it difficult. After SMPS technologies and Ferrites were developed, HV for CRTs was generated by blocking oscillators and step up Transformers at High Frequency AC. Caution Instruction - Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Dual Polarity Analog Output Op-Amps

2008-12-16T08:00:00.000+05:30

When you have to buffer and invert the polarity of mV input levels. This is the circuit you can use, as OP07 has uV offset. R9 and R10 can be 100K 1% MFR or better. Use a symmetrical dual supply. OP07: Ultralow Offset Voltage Operational Amplifier

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Precision Amplifier with Digital uC Control

2008-12-15T15:15:00.001+05:30

When Instruments are designed a analog front end is essential and also as most equipment have digital or microcontroller interface the analog circuit needs to have digital access. The Circuits DACT0008 and DACT0009 are both useful in building instruments which have digital control. This circuit DACT0009 is similar to DACT0008 but gains of upto 100 can be realized in this configuration, this is useful for signal conditioning of low mV outputs of transducers. The gain selection resistors R3 to...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

InfraRed Detector for Proximity Switch

2008-12-14T13:30:00.000+05:30

The proximity switch can work for a wide range of power, from 8v to 18v DC, D3 protects reverse power supply connections, and U1 regulates the supply to +5v , -5v is derived from U2 555 oscillator which serves dual purpose. Circuit Operation The infra red diode D2 detector gets the reflected light from LED and some ambient light, The forward voltage drop of D2 will vary with the amount of light falling on it. Ambient light causes a DC component and the pulsing light from D1 causes an AC...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

InfraRed LED Flasher for Optical Switch

2008-12-14T12:30:00.000+05:30

This circuit is used to detect objects by reflected infrared light. It can be built into a cylindrical enclosure just like an inductive proximity switch. This is also useful as a level detector for colored liquids like oil. This has some immunity to ambient sunlight as it detects ac pulses. IC 555 is used as an astable oscillator and it flashes the Infra red LED D1 at a high speed, The object close to this LED reflects the light along with the ambient light which may also be sunlight. IR...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Precision Attenuator for Digital uC Control

2008-12-11T04:55:00.000+05:30

When Instruments are designed a analog front end is essential and also as most equipment have digital or microcontroller interface the analog circuit needs to have digital access. The Circuits DACT0008 and DACT0009 are both useful in building instruments which have digital control. Precision Attenuator with digital control The Circuit DACT0008 is a programmable attenuator and the digital control can be a remote dip switch, a CMOS Logic Output like the A-B-C-D outputs of a decade counter, or an...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Square and Triangle Opamp Oscillator

2008-10-22T09:51:00.000+05:30

Here is the circuit of a Op-Amp based Square Wave Generator. One of the main application of this is in a Simple PWM circuit and Triangle Opamp Oscillator. The Slope of the Triangle wave is compared with a DC Level to derive a pulse width or On-Time proportional to a Voltage. This On-Time proportional to voltage is for a fixed oscillation rate based on C2-C3 and R15. The C2-C3 form a Unpolarized cap, This type is also used in crossover networks in speaker boxes. This is because, a plastic 4.7...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

2N2646 based Voltage controlled SCR Pulser

2008-10-15T14:00:00.000+05:30

A Center tap 50Hz Step Down Transformer with two diodes is used to get a train of Positive Sine Pulses at 100Hz which is applied to Q6 base via R51. 2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling. This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

AC-AC-SSR Solid State Relay

2008-07-03T17:25:00.000+05:30

This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this. A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

DC-DC SSR Solid State Relay

2008-07-03T14:30:00.000+05:30

This is a DC Input DC Output SSR Solid State Relay. It was made for Printing or Photo Processing Equipment. It has an optical isolation and can be used for inductive loads. The R1 Limits current and Z1 and D1 protects. The 2N3904 limits current in the Opto-Led. When the LED in CNY17-3 turns on, the Light passes thru a electrically insulating area and falls on the photo-transistor in the opto-coupler. This transistor conducts biasing Q2 PNP power transistor. Then Q2 drives Q3 to saturation,...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Normally Closed AC SSR

2008-07-03T14:08:00.001+05:30

This is a Normally Closed PCB Mount SSR. That means when DC Control input is low, the triac is ON, the output passes the load current to turn on small heater-motor-lamp or a bigger contacter-drive etc. When input DC is high the output is OFF. This is also Optically Isolated from Mains. A Microcontroller output which is buffered by some driver can drive this relay. It is better that in big systems these SSR Modules can be on another PCB, to avoid mains wiring near Logic circuits. But this...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.

Flashing Mains Neon Lamp

2008-04-10T16:29:00.001+05:30

Here is a Neon Flasher circuit (untested) for a user request at Elex Quna. This can be built into a switchboard or a gadget for indicating Live Power. D1-C1 form a simple half-wave rectifier, The Cap charges to peak voltage and can store charge for a long time if there is no bleeder. So while building it take extra care. This forms a DC supply across C1. C1 is a Plastic High-voltage cap, IN4007 has a 1KV rating, so it is ok for 230V rectifier. R1 Charges C2 and when C2 reaches 60-80V...

This post is a snippet, to see the full content visit this blog or http://www.dapj.net/. The blogs are listed at dapj Web.