voltage comparator

[mantyi themba]

please assist me in the following circuit. I have a problem with the comparator it does not respond to the input voltages. I have kept an inverting input (pin3) constant at 4.04V, and non-inverting input is varying between 3.31V when IRX1 is not receiving and 6.66V when IRX1 is receiving. suppose I get high at pin7 when IRX1 is receiving and low at pin7 when IRX1 is not receiving. the comparator I used is LM311. your help will be highly appreciated

 

[duke37]

T3 inverts the signal so high input gives low output at pin 7.

T4 and T5 do nothing except drop the impedance, this is not necessary. They can be removed.

Most comparators need a pull up resistor (R15) but R16 pulls it down, which will win?

 

[KrisBlueNZ]

Hi there!

I found the project at http://electronicsproject.org/safety-guard-for-blind/

Most of the circuitry shown in the receiver section is not needed! The TSOP1738 infra-red receiver/demodulator already contains all of the required signal processing, and produces a clean logic-level output. It just needs a pullup resistor and a transistor to invert the signal, and you can feed it straight into the microcontroller.

 

[duke37]

Could the signal inversion be done in software so eliminating Q1?
Changing the complicated circuit to a piece of wire seems quite neat.

 

[BONGIE]

Hi there!

I found the project at http://electronicsproject.org/safety-guard-for-blind/

Most of the circuitry shown in the receiver section is not needed! The TSOP1738 infra-red receiver/demodulator already contains all of the required signal processing, and produces a clean logic-level output. It just needs a pullup resistor and a transistor to invert the signal, and you can feed it straight into the microcontroller.

View attachment 17317

thank you Sir i just did it and its working. thank you alot

 

[duke37]

You could add a PNP transistor to the output, base to base, emitter to emitter and collector to ground. This would protect each transistor and discharge the capacitor when the control is turned down.

A fairly fat transistor would be required but a heat sink should not be necessary unless you are a compulsive knob twiddler.