Author Topic: Discrepancy between a circuit diagram and a photo of the hardware., do  (Read 955 times)

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Offline makermanTopic starter

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Hi, there's a small circuit i want to make, i have the diagram but i also have a photo of it and in the photo there seems to be an extra resistor, what might it be for?

The circuit is for a mega2560 to drive a pulse motor, a hall sensor is used to get frequency and the circuit pulses the coil that drives the motor.
 

Online Doctorandus_P

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Re: Discrepancy between a circuit diagram and a photo of the hardware., do
« Reply #1 on: February 16, 2019, 03:35:34 pm »
It's very near to pin 1 of the opto coupler, and therefore probably to limit the current through the Opto's LED.
 
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Offline makermanTopic starter

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Re: Discrepancy between a circuit diagram and a photo of the hardware., do
« Reply #2 on: February 16, 2019, 03:58:08 pm »
Thanks Doctor, are you referring to the lower resistor in the photo ?

 

Offline makermanTopic starter

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Re: Discrepancy between a circuit diagram and a photo of the hardware., do
« Reply #3 on: February 16, 2019, 04:07:01 pm »
Oh no i see now, the lower one is across opto and diode.
 

Offline rstofer

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Re: Discrepancy between a circuit diagram and a photo of the hardware., do
« Reply #4 on: February 18, 2019, 04:02:02 pm »
Hopefully, it is series with the LED portion of the optocoupler.  The schematic seems to indicate that no such resistor exists, probably with the thought it is located elsewhere.  Nevertheless, the resistor is necessary.  Probably a low value, less than 1K I would guess.

The lower resistor in the photo is clearly 20k which is the value of R1 in the schematic.
 


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