Car park sensor --> need help with component functions

[Lars1408]

Hi I'm a student Electronics ICT and I have to explain the following circuit to my teacher.
I'm not sure what the function of these componnets are: R8, R9, R11, C5, C3.
Does anyone know? IC2a is an amplifier and IC2b, IC2c and IC2d are comperators.

Another circuit has an IR transmitter that will transmit against an object...it wil be received by D2--> that signal will be detected by D4, C4 (peakdetector)
the output voltage from the amplifier will be proportional to the distance from the object. The comperators will compare the constant voltage at the +input to the variable voltage at the -input...this will cause the right leds to light up at the right distance.
For example 3leds for 5cm and 0leds for 20cm

 

[AnalogKid]

First, all 4 sections of an LM324 are operational amplifiers. a is configured as a trans-impedance amplifier, while b, c, and d are configured as comparators.

I'll give you this one - C5 is a simple bulk filter capacitor to keep noise and voltage dips caused by transient currents off of the 12 V running the circuit. Don't let it's location in the schematic fool you, it is not directly related to the IC2d circuit.

So, comparators compare - what? All three comparators have one input driven by the received signal, and you already stated that that signal increases and decreases with range. To pick off three different range points, what do the comparators need on their other inputs?

ak

 

[Lars1408]

First, all 4 sections of an LM324 are operational amplifiers. a is configured as a trans-impedance amplifier, while b, c, and d are configured as comparators.

I'll give you this one - C5 is a simple bulk filter capacitor to keep noise and voltage dips caused by transient currents off of the 12 V running the circuit. Don't let it's location in the schematic fool you, it is not directly related to the IC2d circuit.

So, comparators compare - what? All three comparators have one input driven by the received signal, and you already stated that that signal increases and decreases with range. To pick off three different range points, what do the comparators need on their other inputs?

ak

Thanks for the response...
This is the site where I got the scheme from-->
http://www.circuitstoday.com/parking-sensor-circuit/comment-page-1#comment-684371

""The output of peak detector is given to the inputs of the other three comparators IC2b,IC2c and IC2d inside the IC2 (LM324).The comparators switch the status LEDs according to the input voltage their inverting inputs and reference voltages at their non inverting inputs. Resistances R7 to R10 are used to set the reference voltages for the comparators.""

So what I understand from this is that the Reference voltage is compared to the other input voltage comming from the amplifier IC2a, no?

 

[hevans1944]

Yes. And there are three reference voltages, all different, one for each comparator to compare against the signal from IC2a. Can you calculate what these three reference voltages are?