I have a vintage Stewart-Warner Tachometer (760AX) that requires a sending unit that fits under the distributor cap. Senders are essentially nonexistent at this point in time, so I am posing this question to the group: Does anyone know what waveform the Stewart-Warner sending units put out? Or the converse: what waveform does the 760AX tachometer need in order to function? Given current technology - no pun intended - it would undoubtedly be possible to generate the appropriate waveform if only I could learn what it is. Then, I would not need to find the extinct sender. I hope someone can help.
I've never worked with that exact model, but have with some of a similar vintage in marine applications. I think the sender output would be square wave...I'd start at about 5 volts and go up until the tach head responds appropriately. If it doesn't like the square wave you'll know pretty soon, but the low voltage won't hurt anything.
I've been working in the same thing since my sending unit is kaput google "555 tachometer schematic" etc and you will find a bunch of schematics using the ne555 integrated timing circuit that will translate the signal to the tach. I've wired a few if the schematics on a breadboard with marginal success. The best schematic worked but was sluggishly responsive. I'm not savvy enough to know which resistor and capacitor values to change to get to something acceptable. I'm in the process of trying out the other schematics I've found and if I come across one that works I will share the results. I was also thinking of having some PCBs made to share with others once I settle on a working circuit. Good luck and let me know if you're successful! Posted from the TJJ App for iPhone & iPad
I came across this one on ford barn: http://www.electroniq.net/555-timer-circuits/tachometer-circuit-using-555-timer.html Didn't work accurately or responsively for me but might for you. Posted from the TJJ App for iPhone & iPad
I replaced a sender for a Sun tach with a 555 circuit described in my web site article: http://myplace.frontier.com/~wgmumaw/Sun%20Tach/Sun%20Tach.html If the SW tach operates on a similar current it might work for you.
I am currently trying this one out on the breadboard. Thanks for setting this up. Don't be surprised if I PM you with a couple questions.
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