tommy

I am building a basketball scoreboard for my son. I have an old PLC which I yanked out of a machine from work but I only had enough outputs to drive 4 per number. The 4511 seemed like the answer since it only needs 4 inputs to convert to 7 segments. I have the thing built and wired but it keeps burning up chips. I assume I have something calculated incorrectly with the circuit and could use some help. I am a PLC / electrical guy with a foggy memory of my electronics schooling and could use someone to double-check my circuit. Briefly, I'm using 4 relay outputs on the plc to feed the four inputs on the chip with 10K resistor in parallel to ground on each. I'm using 12.5 vdc. The output of the chip is feeding small circuit board type relays with a resistance of 720 ohms. The relays in turn are switching power to the lights (I hacked up our Christmas tree lights because they were free - trying to keep the thing on budget, ha ha). What is happening is this: By changing the combination of the four inputs the outputs respond properly, but after only a few tries the relays start buzzing and everything freaks out. I'm assuming the chips are toasting. Do I need to review the resistor values to lower the current? According to the spec sheet on the 4511 the max output current is 25ma. Would that be total for all 7 outputs or per output? I realize this is kind of a bonehead project compared to some of the high tech things I'm reading about on this forum, but to my 10 year old son this is the big time and I hate to let him down. I'm much more at home controlling machines with PLC's (that's what I do) and am humbling myself to the electronics wizards I hope to meet to find some help...