Automated counting system

[joku]

I'm working on an automated counting system for work. The basic premise is I would be able to drop a part down a chute, the part will pass through an IR beam, and a counter will increment. But there are times when I'd have to drop two parts down the chute at once. Trying to put this into an easy to use unit is causing a few problems.

I already have a counter and it requires the following signals to increment:

A ¯¯¯|__|¯¯¯¯¯
B ¯¯¯¯¯|__|¯¯¯

To decrement, the signals are switched.

I've been able to work out a way to generate this signal from a single tripped sensor by using a pair of 555 timers. But, I don't think it's incrementing 100% of the time.

When I drop two parts down the chute, there's no way to ensure the parts don't pass through the beam simultaneously. To correct this problem, I have the first timer set to last ~2 seconds so the second part isn't registered. But now I have to generate two consecutive output signals given a single input. Using my current method I can't see a way to increment twice without adding in two more timers which is just going to drive up the size, complexity, and cost of the circuit.

So I figured there had to be a better way. Is there some IC out there that will take a single input signal from my sensor and generate the output signal I need either once or twice depending on whether a second input signal is in a high or low state?

 

[BobK]

You could build such a thing, but how do you know whether 1 or 2 parts were dropped?

Bob

 

[jcurrie]

are the parts of a uniform size ?

jc

 

[joku]

I'll give a little more information about the specific application. I work in a foundry. We have to grind excess metal off of the parts that we make before they get machined. The parts vary greatly in shape and size, ranging from roughly .5"X.5"X.25" up to around 5"X5"X3". They also vary in number from anywhere between 50 and 5000 of a part in one bin. Some of these parts can be worked two at a time on the grinding wheel, others have to be done individually.

The way things are set up, a bin full of one kind of part is dumped onto a tray next to the grinding wheel. The worker grabs the part (or parts) from the tray, grinds it, and tosses it into an empty bin roughly three feet below and three feet away from the grinding wheel. Then he presses the button on a mechanical tally counter like this:

With this project I aim to replace the manual counting, thereby increasing speed while also reducing counting errors. Since multiple people will be using this, I want to try to keep it as simple and intuitive as I can. I figure I'd have a power switch, a reset button, a button to manually increase the count, a toggle switch to go back and forth between incrementing by 1 or by 2, and a toggle switch to switch between counting up and counting down (I figure a simple DPDT switch to flip the A and B signals I had described in my first post).

I've gotten to where I am so far in this project using stuff I was taught about a few years ago. But I was never taught about things like controllers or PALs, and I think it's something along those lines that will do what I need with a single IC. While I think something like that would be ideal, if it's not possible or practical, I just now thought of a way to implement the two output signals from the single input. I could use a bistable to send a second input signal after receiving the first output. So I have a backup plan.