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Please help (design)

by khumalop3
Tags: design
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Mar9-07, 02:13 PM
P: 1
I'M required to design an electronic system to be used to count objects in a
packaging process as they pass on a moving conveyor belt. The system consists of a power supply, optical detectors, a signal conditioning circuit, digital counter circuits, and displays.
PLEASE HELP whith how to desing a signal conditioning circuit and digital counter circuits
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Mar9-07, 03:18 PM
P: 87
The one way to do it is to do the following:

Let's assume that the optical sensor consist of two parts, transmitter and receiver, transmitter constantly sends a beam of light (or whatever) towards the receiver, hence receiver gets all the energy, let's assume that this state is logical "1".Once the object is in the between, no energy gets to a receiver, hence the output is at low state, logical "0".

The only thing you're required to do is to count those 1->0 or 0->1 (you'll have to decide) transitions, in order to get the number of objects that has passed. A simple counter implemented using flip-flops could be used, where the output is fed directly to some BCD display via appropriate logic. You can find discrete implementations of the counters searching the Texas Instruments (click here, to go directly to counters page at or Analog Devices sites.

Now, the output of receiver is not perfect, since it is a sensor, so the output won't have those perfect 0's and 1's, hence the output of the sensor should be coupled with a comparator opamp, this way you'll be able to sort out between 0's & 1's better (distinguish level transitions).

Since you didn't mention anything about the number of objects, I'm guessing that there will be a finite number of them, so when you've determined the number of objects so you can find out what kind of counter you'll need (how many bits). Otherwise, when you don't know anything about the number of objects, you'll need a micro controller of some kind in order to save and add the number of objects, before resetting the counter.
Mar9-07, 03:46 PM
berkeman's Avatar
P: 40,964
And another part of the signal conditioning should constrain the sensor circuit's bandwidth to match the expected behavior of the items passing by on the conveyor belt. How frequently will the signal change (how wide are the objects, and how fast is the belt)?

Also, think about what you want your circuit to do if the belt stops right when there is a can in line with the beam....what does that tell you about the kind of filter you should be using in that signal conditioning circuit? Can you think of a reason why you might want to have a belt speed sensor as part of the processing circuit? Are you familiar with the concept of hysteresis, with respect to the comparator component that antoker mentioned?

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