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How to control a counter with separate start and stop pulses?

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LAN_403

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Sat Apr 22 2006, 08:36PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay, i almost finished my new project, but now i run into problems.
i finished my counter, my 1mhz crystal oscillator and my photogates, everything is fine . but now i dont know how to wire the flip flop or something to get the counter started when the projectile passes the first photogate, and to get it stop when it passes the second photogate. im not a pro in digital electronics and especially not in flip flops, so i need your help.

please dont come up with, build it with a pic, or measure it with your soundcard (i have no pic yCÂ´s and not the equipment to prog it, and i have no computer in my garage))

rupidust

Sat Apr 22 2006, 09:41PM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

I want to see thee schematic, mostly which counter IC is being used. I have not done flip-flop and counter ICs in years, but can use a refresher experience.

Yeah I know, no PIC. Still, here is a chrono with pads ready to except photogates, led indicator, switch, power, and RS232 interface wires. Every measured time is stored into EEPROM and can be later retrieved so that chrono can take readings either attached or not atttached to computer. Also a history of shots upto 10 is saved in EEPROM and constantly update like a rolling counter.

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Sat Apr 22 2006, 10:11PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, thats quite impressive but its does not answer my question.

i use a counter decade of 6 cd4026 cmos ics , oscillator is a redy made 1,0000000mhz crystal ocillator

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Sat Apr 22 2006, 10:19PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Ok, so do you have any JK flipflops?

If you do I believe it is a pretty simpe thing, you just take the 1mhz signal, feed it into the clock input, hook up one photogate (use it as half a resitave divider to get a signal that you can feed directly into the flip-flop) to the set and the other one to the reset...

I think that was all you need to do, I haven't looked over my notes in ages...

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Sat Apr 22 2006, 11:42PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yes, i have the 74hc109 on hand, iÂ´ll try it tommorow to see if it works, thanks

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Sun Apr 23 2006, 12:42AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Looking at my notes I realised that I am more of a genius than I thought

I used a quad nand gate chip, with one half wired as a rs flipflop. The set/reset was the photogates, and the output was wired to the reset of the counter. If you can't use the reset of the counter then you could use one of the nand gates to gate the signal from the clock; and you still have a free gate

I also wired a hard reset button from the reset input to ground so I could make it stop counting if it didn't trigger proberly (since there was like 3k in series with the photogate I didn't have to worry about shorting everything out, you could add a 1k resistor in series with the reset input of the gate is you went for the opamp method)

Just putting more options on the table...

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Sun Apr 23 2006, 09:35PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

hehe, thank you very much, i got it and it works just fine

rupidust

Sun Apr 23 2006, 09:45PM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

Good. What did you do to get it working? Is it working for both long and short length projectiles or just long length projectiles? Long meaning the projectile length is longer than the distance between the two detectors and short meaning the length is shorter than the detectors.

Is this what you are doing or did? This schematic shows how a long length projectile will work, but a short length projectile causes the counter to only take a measurement of Gate1. Or did you use another method?
http://www.geocities.com/rupidust1/img-7segcounter.gif

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Mon Apr 24 2006, 12:23AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

My design was designed for 'short' length projectiles... Just as long as you use a flip flop that triggers on the rising edge it should work for all of them...

I don't see why you would want to use the sensors so close that they are shorter than the projectile, wouldn't that give really crappy accuracy?

rupidust

Mon Apr 24 2006, 01:04AM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
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Posts: 85

... wrote ...

I don't see why you would want to use the sensors so close that they are shorter than the projectile, wouldn't that give really crappy accuracy?

Yes and no. That depends on projectile length and time scale. Some projectiles are > 10 cm long. In the case of a 10 cm distance between sensors, the accuracy would not be crappy sence the time scale is in microseconds. The longer the distance between sensors and the smaller the time scale, the better the measured time. Projectile length makes no difference.

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