# Trigger circuit

Discussion in 'The Projects Forum' started by libbresse, Mar 7, 2009.

1. ### libbresse Thread Starter Member

Mar 6, 2009
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I'm trying to build a highvoltage distrubutor to my dragrace snowmobile. What I figure about now is how I should pick up the trigger signal from my hall sensor. It's a two wire sensor type. Could someone point me to the right direction

2. ### libbresse Thread Starter Member

Mar 6, 2009
12
0
Alberto: The sensor I want to use is from MSD:

http://www.msdpowersports.com/pwc_triggers.html#snowmobile

The thing is it's no specification on the sensor available. But I will test it with a logger to see what it sends out.

I was thinking of a comparator with a voltage or current threshold. I have read the specifications on a lot of comparators, what I don't understand is how to set a specific threshold on the comparators ? I am not that used to build own circuits so to speak

3. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Are you converting a sled to electronic ignition, changing an existing ignition system, or "other"?

What model engine/sled is it, or do you have This?

Comparators swing their output to the polarity of the greater input. If powered by 5V and ground, when the + input is higher than the - input, the output will be high/5V, when the - terminal is a higher voltage than the + terminal, the output will be low/0V

To compare against a voltage, usually a voltage divider is set up for the level on one input, and the signal is on the other input. Which input is used for the signal depends on if a high or low value is desired when the threshold is met.

Last edited: Mar 7, 2009

Mar 6, 2009
12
0

Mar 6, 2009
12
0
6. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
At quick glance, your circuit has voltage dividers on both inputs, with the additional squarewave source. Try simplifying it using two 10k pots, both with one end to power, and the other end to ground. One wiper to each input. Then simulate one moving with the other centered, and vice versa. I haven't used OrCad/LTSpice, so am not sure if that's a simpler simulation. With the existing circuit, add two additional probes on the two inputs to see what the input voltages are, if one never "passes" the other, the output will remain the same.

Below is a link to a good article from Maxim, which also covers a topic (hysteresis) you may need in the ignition circuit as well. In addition, it shows schematics for the input to be both on the inverting and non inverting inputs, with diagrams of the input/output of each. It should expand your understanding, as well as the related links at the bottom of this file. They are all from Maxim and "safe":

http://pdfserv.maxim-ic.com/en/an/AN3616.pdf

7. ### libbresse Thread Starter Member

Mar 6, 2009
12
0
thatoneguy: Thank you allot for your input I'm currently working real hard I will test when there is less at work