I posted on this forum before with a question about a circuit; I got a few responses, and took them into consideration. From these, I was able to build a working breadboard circuit, and a working circuit soldered on protoboard.
I figured the next step for me would be to print the board. I took my existing schematic (which I had copied exactly when soldering together the protoboard) and converted it into a PCB, before printing the PCBs.
The problem I have is that the circuit doesn't work on the pcb.
The section of the circuit that doesn't work should turn on/off 5v 20mAh of power, using a pc817 optocoupler controlled by a 5v Pro Micro.
Schematic (only of this section):
The biggest problem I can think of is noise produced by other components or nearby traces on the board. Is this a possibility? Here's a picture of the surrounding traces:
Anyone have any thoughts on what the issue could be? Or is it something obvious I'm missing? All responses are greatly appreciated, and thanks in advance for your responses.
Hi,
Do you have a DMM to trouble shoot your PCB?
If not you really need to get one.
Have you written some simple code that just operates the opto-couplers to check your circuit?
Can you measure the 5V output of the Arduino?
Can you measure the voltage across the diode input pins of the opto-coupler.
Are your SMD resistors the correct value?
To help with seeing your circuit operating, in hindsight, a LED in series with each of the opto LEDs would have helped you see if the opto is being controlled.
After a quick google search, I believe that testing continuity using my multimeter is using a DMM - I've done this, and made sure all the solder joints and connections are made.
I have written simple code to test everything; (because I used the same exact schematic for my protoboard test, I have confirmed that the code works) however, signal doesn't seem to be passing through the non - diode, or output side of the optocouplers (I'm not sure what the correct phrasing for this is) on the PCB. As mentioned above, that is only a small part of my complete circuit; the rest consists mostly only of buttons and what the optocouplers turn on and off. I have made sure that all the power going into and out of the optocouplers is within their ratings, as well as made sure that the optocouplers work properly (I tested them in a simple LED on - off switch on a breadboard before soldering them to the board).
The 5V of the arduino is consistent, using power from my computer's USB port, and there is no voltage across the diode pins of the optocoupler (I'm assuming this is what it should be, to make sure the small infra red LED inside the optocoupler isn't blown out).
Using an LED in series with the optocouplers is a smart idea -- I'll give that a shot.
ralipy:
The section of the circuit that doesn't work should turn on/off 5v 20mAh of power, using a pc817 optocoupler controlled by a 5v Pro Micro.
mAh is a measure of battery capacity, not power or current. Optocouplers are for signals, not power.
What is the current being switched? If its more than a few mA its not going to be feasible using an
optocoupler. Opto couplers vary a lot between individual devices, the current transfer ratio for
the PC817 has a range of +600%/-50%, so you may just being seeing differences in the
transfer ratio between batches.
ralipy:
there is no voltage across the diode pins of the optocoupler (I'm assuming this is what it should be, to make sure the small infra red LED inside the optocoupler isn't blown out).
I would have expected a ~1.2V across the diode pins, corresponding to the datasheet stated VF.
Hi,
Can you draw a diagram of what and how you have the 5V 20mAh what ever connected to the output of the opto-coupler please?
How do you know that signal/current is passing through the diode side or input side of the opto?
Did you measure the voltage from gnd to the output of the Pro Micro that feeds the opto?
Measure when the output is supposed to be ON or HIGH and OFF or LOW.
Can you post a picture of your project please so we can see your component layout?
