SOLVED DIY Dual State Relay issue

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Bumfluff101

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Taking inspiration from a number of forumites I'm working on a footswitch project using an ATtiny85 to control two non-latching relays (FTR-B4CA4.5Z), and I've hit a wall that I can't seem to figure out. The logic involves a short press toggling one relay (Engage/Bypass) and a long press cycling/selecting the other (Drive 1/2).

The Problem: I ordered some pcbs and populated everything but the relays do not click when they are supposed to in the circuit. Using a bit of Gemini I've tried to run diagnostics, but things seem to be working - thought I'm now doubting if the circuit is actually right o_O I'm hoping a fresh pair of eyes might spot something I've missed.

Setup:
  • MCU: ATtiny85 running at 1MHz internal clock.
  • Relays: 2 x FTR-B4CA4.5Z (4.5V non-latching).
  • Driver: 2N3904 NPN transistors with 4.7kΩ base resistors and 1N4148 flyback diodes.
  • Power: 9V supply regulated down to a stable 5V.

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leadfoot said:
So, you've now entered the world of embedded systems. :)

Are you sure it isn't the code you're running in the ATtiny85?
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Lol yep

I think the code works, as standard there is 5v on each of the coil pins, on pressing the switch, pin 1 on the really drops to about 169mv which should effectively ground it and switch the relay state but it..er .. doesn't
 
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Just an idea, but have you attempted to simulate what you want to do manually? For instance remove the ATtiny from the equation completely and have 5v running to two on/off spst one for each relay. That way you can determine if it's the circuit or your code.
 
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Any chance you have the coil polarity reversed?

If pin 8 has a stable 5V and pin 1 is transitioning from 0V / 5V the relay should be closing.... unless the polarity is backwards.
 
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