I need a pulse generator. Namely one that can generate the same singnal a tachometer runs off of. Wich if i'm correct is the ground of a curciut? Thanks
http://www.joliettech.com/avtron_tachometers-encoders-rotary_pulse_generators.htm (http://"http://www.joliettech.com/avtron_tachometers-encoders-rotary_pulse_generators.htm")
http://www.avtron.com/tachs.htm (http://"http://www.avtron.com/tachs.htm")
anything like that?
Those all seem a little to industrial. Plus the Rotary Pulse Generators look to be something that is hooked to a machine to count revolutions or somthing.
I'm looking for a small simple circuit that can pulse from say 0 to 50,000 Pulses per minute. Wich would be 6250 Rpm for a v8.
I'm wanting the device to have a readout of how many pulses it is actually putting out as well as an easy means of adjusting them. Say a potentiameter.
building adjustable tach for 4 cyl, 6cyl and 8 cyl cars?
1) eBay has a lot of old clunker pulse generators,,, ie
http://cgi.ebay.com/Tri-Phenix-Pulse-Generator-Model-PX4-PX-4_W0QQitemZ7589405189QQcategoryZ97197QQrdZ1QQcmdZViewItem (http://"http://cgi.ebay.com/Tri-Phenix-Pulse-Generator-Model-PX4-PX-4_W0QQitemZ7589405189QQcategoryZ97197QQrdZ1QQcmdZViewItem")
They would have scales on the s, but by the time you include shipping, you are probably around $40 for the cheapest deals.
2) The 555 Timer integrated circuit
This IC is a deicated pulse generator if you can get a solderless breadboard & some electronic parts, the 555 timer IC is an easy circuit to build. The R1 potentiometer shown in the link below could pretty much adjust to 0-833 Hz (divide your RPM's by 60 to get frequency in Hertz). With fixed capacitors and an ohm meter to measure the variable resistor you could make an RPM scale.
http://www.electronics.50g.com/cosc555.htm (http://"http://www.electronics.50g.com/cosc555.htm")
You could buy this 555 timer kit (user manual is online - you want to run it in "astable" mode) http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=UT5 (http://"http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=UT5")
As long as you have a pulse generator, it can be used to drive a transistor that would provide an open collector to ground the circuit as you wanted, - although I thought the tach signal is actually pulses of voltage rather than a closing switch to ground.
The tach signal is actually similar to AC. I say "similar" because true AC would go from, say, -12 to +12 volts while the tach signal goes from 0 to 12. The ignition module provides a pulsing ground, but when the ignition module is not "grounding" the power is backfeeding through the coil, so if you were to measure the voltage at the tach terminal on the coil it would show a ground (0 volts) while the igntion module is "on" and a positive (+12v) while the igntion module is "off" (the voltage may actually be slightly lower than 12 due to the resistance inside the coil).
The 555, like Bondocougar said, puts out a pulse, and it switches between positive and ground like the tach signal (as opposed to between power and nothing).
Take a look at http://www.uoguelph.ca/~antoon/gadgets/555/555.html
its based on a 555 ic which is very common. It'll do just about anything.