How Do I test the Start Sensor Circuit

DIY timing systems
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Kurt Wylde
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How Do I test the Start Sensor Circuit

Post by Kurt Wylde »

Hello
I am building the circuit on this site. I am now ready to "Test the Quad Comparator Outputs". My feeble brain needs a more detailed description of doing this.

Pic of circuit:
Image


The instructions state to test for voltage across the lane's output; could someone please describe where each lane's output is on the circuit?


Thanks and Merry Christmas!
NealOnWheels
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Re: How Do I test the Start Sensor Circuit

Post by NealOnWheels »

From the LM339 datasheet (http://cache.national.com/ds/LM/LM139.pdf) look at the top of page 16. The diagrams show the comparator outputs as pins 1, 2, 13, 14. Use a voltmeter with the positive lead on these pins and the negative lead on "ground" - pin 12 or another convenient point on your board. Without the schematic I don't know what you should measure. Can you provide a link to the schematic you are using?

I see you are using a prototyping board. These boards are good for temporary testing basis but are not that reliable for a pinewood derby race. Components and wires can easily be jarred loose from a small bump. You would not want to be trying to fix it in the middle of a race. Also in the long term you will likely have "fretting corrosion" issues on all of the tin-tin contacts. Soldering would be a better choice.

I hope this helps.
Kurt Wylde
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Re: How Do I test the Start Sensor Circuit

Post by Kurt Wylde »

I will study that info you posted NealOnWheels and see if I can make sense of it.

The plans I am using are here: http://grandprix-race-central.com/modul ... page&pid=7

I just hooked up the "optional" LEDs between E25-H25, E23-H23, E29-H29, E27-H27, E31-H31. These all light up when I hook up the power, I assume that is intended? If I short Pin1 to ground (on the left comparator in the circuit) the LED at E25-H25 turns off; I assume that is also correct?

Once I figure out the circuit is working I will transfer it to a circuit board and solder it.
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gpraceman
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Re: How Do I test the Start Sensor Circuit

Post by gpraceman »

All of the indicator LED's should be off unless the IR beams are blocked or the start switch is open.

Are you testing while connected to the parallel port? I would suggest that you not hook to the parallel port until you make sure that the circuit is working.
Randy Lisano
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Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
Kurt Wylde
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Re: How Do I test the Start Sensor Circuit

Post by Kurt Wylde »

A more specific question may help me -

The instructions from the website:
To test each comparator output, one at a time, take a small length of wire and connect from the lane/start input of the quad comparator (pins 4, 6, 8, and 10) to ground. The holes at the back of the wire terminals are good for this purpose. Then with a multimeter, or an LED for that matter, test across the wire terminal that correspond to that lane's output.
If I use a jumper wire from pin 4 to ground, what are the two coordinates on the prototyping board that I should be testing with the multimeter? What should the meter read before and after I use the jumper wire?

Thanks.
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gpraceman
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Re: How Do I test the Start Sensor Circuit

Post by gpraceman »

As you ground each of the inputs to the comparator with a length of wire, the corresponding indicator LED should light up. If you don't have the indicator LED's in the circuit yet, then use the meter to test the comparator output to ground, which should read about 5V. If you remove the jumper wire, the output should read 0V.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
Kurt Wylde
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Re: How Do I test the Start Sensor Circuit

Post by Kurt Wylde »

I have removed all the LEDs from the circuit, and it is not connected to the parallel port; it looks just like the picture in the first post.

If I measure the voltage on the left Quad Comparator, between pin 12 (ground) and pin 2 (Output 1) the meter reads .1 volt. Is that a problem?

When I attach the jumper wire from pin 4 (Input 1-) to ground, the voltage between pin 12 and pin 2 reads 4.96 volts, which I believe is correct.

I am concerned why there is voltage between the outputs and ground when I am not grounding the inputs.

Thanks for all the help.
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gpraceman
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Re: How Do I test the Start Sensor Circuit

Post by gpraceman »

That 0.1V will not be a problem. The signals in the circuit will be approx 0V and approx 5V.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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