Friday, May 18, 2018

Precision Amplifier with Digital uC Control

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 Amplifier with 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 R6 can be selected by the user and can be anywhere from 1K to 1M and can also be trimpots for obtaining gains as required by user, the resistor values shown are for decade gains e.g. for an auto ranging DPM.

Precision Amplifier with Digital Control

R1 and C1 reduce ripple in input and also snubs transients, ZD1 and ZD2 Zeners clamp input to +/- 4.7V the input current is limited by R1 lastly C1 and C2 are decoupling capacitors. The OpAmp U3 is used to increase the input impedance so that very low mV inputs are not loaded on measurement, the user can terminate the inputs with a resistor of his choice like 10M or 1M to avoid floating of the inputs when no measurement is being made.

Thursday, May 17, 2018

InfraRed Detector for Proximity Switch

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

Part of - InfraRed LED Flasher for Optical Switch

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 component.

Proximity Switch - Driver Supply

The capacitor C6 blocks DC and only transfers AC pulses if any to opamp amplifier U3A whose gain is set by R18, D9 rectifies the pulses to DC and this DC voltage is used by opamp comparator U3B which drives Q1 through Q2 for an open collector output for relays. LED D7 turns on when relay Output is high.

R14 and R13 can be replaced with potentiometer for threshold adjustment if required.

Connect 12v DC supply to +V and GND Ports, Connect a relay coil Between OUT and GND Ports, you can use the relay contacts as you require to turn on a lamp, heater, fan or motor.

If all connections are ok and ICs are working you should see a +5V at U3 pin8 VCC and around -4 to -5 at U3 pin4 VDD.

See also - Mixed and Interface Circuits

Optical Proximity Switch - Detector


The Optic switch can be used for both reflecting detection (retro reflective) or obstacle detection. The mechanical construction will decide this, for obstacle detection the diodes D1 and D2 could be put in two different tubes and can be kept far apart 2mts+ and both should be exactly opposite each other, any obstacle like a passing person will be detected.

To make a retro reflective proximity switch this circuit is ideal, it can be housed in a cylindrical 30mm by 70mm metal unit with m30 threads and nuts for mounting, both D1 and D2 have to be fitted in the front of this tube on a plastic plug optically insulated from each other yet beside each other.

Tuesday, May 15, 2018

Voltage Doubler with Diodes

This is a Simple Voltage Doubler to boost 3V battery voltage to power some low-power 5V circuits. In needs a Clock input with high fan-out. You can use the 74HCT540 in parallel. Work with the Audio frequency range and see.

Voltage Doubler with Diodes

If you feed a Low Impedance Square wave, like output of 555, which has adequate Source-Sink Punch. to Input A, then it is quite possible you get double the voltage at B on No load.

Mains Voltage Current LED Indicators

There are many designs you can do with just resistors, capacitors, diodes and LEDs. Zeners and Inductors will add to the fun. The Transistor or Zener can make the circuit smart.

Hobby DIY Electronics