greetings!!!
well let me tell you about my problem, i'm taking a laboratory class, called digital systems...and i'm required to design a circuit for my final project, and well i need help, it has to be a reflex tester circuit, it should test the reflexes of a person, by meassuring the time between a led diode turning on and the pressing of a push-button, and also the pressing of 2 push buttons, and it should show the time, in 2 BCD displays...

well i don't know if my english is good enough but maybe someone can give me a hand, i'm pretty certain i should use a 555 IC for timing but not sure as to what else to do...

cheers

 

dear you massege isnot so clear so can you describe your prob briefly...

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You need to measure time so what circuit can do such a thing? The most obvious way is to measure the number of cycles of a known AC signal. For example, if you had an oscillator whose frequency you know to be always exactly 1 KHz you could use this as a sort of "clock". This clock has an output that goes through one cycle of "high" then "low" and so on in exactly 1/1,000 second, or 1 millisecond.

Imagine that you could pass this clock through a gate. If you can open and close the gate using the LED and the pushbutton, you can count the number of clock pulses that pass through the gate and this count would be your time measurement.

You would need to arrange so that when the LED turns on, the gate opens, passing this clock through the gate. Then when the button is pressed the gate is closed and no more clock pulses pass through. You could then measure the exact time by counting how many cycles of the clock passed through this gate. Then, you can display this count by using a display circuit. If you simply display the counted number, the display would be the valid number of milliseconds it took for the operator to react to the LED and close the switch.

Now, can you draw a simple block diagram showing what I have explained? If you do, then we can discuss what detailed circuits will fit into that block diagram.

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RadioRon

 

well yeah the circuit should meassure, or more like show, by means of the bcd displays, the number of seconds that takes for the pushbuttons to be pressed after the led turns on, the led control is not an especified condition of the project...

 

Why not just use a microcontroller one output for the led and take the pushbuttons into two interrupts. It would be very few parts: power supply, led, two buttons, display and some passive components. You could even get one with an internal oscillator to eliminate those components. I don't know if this approach goes with the class objectives, but it is the way I would probably go.

 

i think that's a rather advanced approach to the thing, since this lab has been about the use of gates, and boolean logic

 

RadioRon has lead you in all the right directions there, and he's left it open for you to return for more discussion later provided you're willing to put some work up front and think about a block diagram.

That's quite a decent offer, so if I were you I'd get busy drafting up a block diagram of the system!

Brian

 

Fair enough, just a thought, good luck with your project.

 

I second that notion..... Good advice there radio.
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