Hi. Im designing a circuit that uses a 40 pin PIC chip to control a bunch of lights. Each light has its own transistor on the board. I would like some method of testing these lights to be built into the circuit. The bulbs dont have to be working during testing.

Ive come up with a few ways that might work

I thought about having a circuit to measure the current that each board is using (the simple resistor style one Ref: Measuring Volts and Amps digitally. If i measure the amps its using while all outputs are off then turn each output on individually and measure again. If there is no significant increase in current then the bulb has blown. This one has the added bonus that the bulb being tested can be turned on. The problem i see might be that the bulbs dont use enough current to distinguish between the bulb being on and the chip using a little more power for something etc.

Another idea was to have a relay that switches the common wire of the lights over to an input pin on the chip (with a resistor because the bulbs are about 7-12V). Then turn each bulb on individually and check if the input pin goes low (transistors are NPN). I would need a resistor to make the pin high when no outputs are on. The problem i see here is that the bulbs will effectively become resistors so the biasing resistor needs to be big enough to pull the pin high but small enough to allow it to go low when an output is turned on

The power to the board will be DC 12V (regulated for the chip). There will be capacitors elsewhere to smooth out the DC ripple and some extra on the board itself.

What i want to know is what do you think? Which method would be overall best taking into account number of pins used, reliability, cost etc? Does anyone have a better suggestion?