Hello all,
As the title states, I've just moved a project from a development board to a custom made PCB. Unfortunately I can't provide an exact schematic, as I'm not permitted to, however I'll do my best to explain.
It uses an ATTiny261. 4 inputs (each a switch), 3 outputs (2 assigned to a bi-color LED and one to a relay driver circuit).
The relay driver circuit includes a 1kΩ resistor from the μC output pin to the transistor base, a 4.7kΩ (what I had on hand) acting as a pull-down from the transistor base to ground and the relay has an activation current of about 100mA and resistance of 85Ω. I calculated the 1kΩ value using a worst-case scenario of a 45 hfe transistor and 150Ω relay.
I use a common 5v low dropout regulator with capacitors on both the input and output rails.
I hope that provides enough background information about the circuit. Now, the software and problem.
The software is simple enough. If one of the switches is pressed, turn on the red LED and turn off the green. If another switch is pressed, turn off the red LED and turn on the green. This works correctly on the development board.
On the PCB, however, its very erratic; both when I have the switches controlling the LEDs and when I have it controlling the relay. It seems any movement whatsoever on the PCB will cause a change in the output... sometimes even lighting both the red and green LED. I can literally breath on the circuit and change the color of the LED. I've checked with the multimeter again and again: there are no shorts.
I'm away from work for the holiday and don't have access to spare parts so that I can build another board up from scratch, so I need to debug this one. I'm completely lost as to where I should begin troubleshooting, does anyone have an idea?
As the title states, I've just moved a project from a development board to a custom made PCB. Unfortunately I can't provide an exact schematic, as I'm not permitted to, however I'll do my best to explain.
It uses an ATTiny261. 4 inputs (each a switch), 3 outputs (2 assigned to a bi-color LED and one to a relay driver circuit).
The relay driver circuit includes a 1kΩ resistor from the μC output pin to the transistor base, a 4.7kΩ (what I had on hand) acting as a pull-down from the transistor base to ground and the relay has an activation current of about 100mA and resistance of 85Ω. I calculated the 1kΩ value using a worst-case scenario of a 45 hfe transistor and 150Ω relay.
I use a common 5v low dropout regulator with capacitors on both the input and output rails.
I hope that provides enough background information about the circuit. Now, the software and problem.
The software is simple enough. If one of the switches is pressed, turn on the red LED and turn off the green. If another switch is pressed, turn off the red LED and turn on the green. This works correctly on the development board.
On the PCB, however, its very erratic; both when I have the switches controlling the LEDs and when I have it controlling the relay. It seems any movement whatsoever on the PCB will cause a change in the output... sometimes even lighting both the red and green LED. I can literally breath on the circuit and change the color of the LED. I've checked with the multimeter again and again: there are no shorts.
I'm away from work for the holiday and don't have access to spare parts so that I can build another board up from scratch, so I need to debug this one. I'm completely lost as to where I should begin troubleshooting, does anyone have an idea?