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RPM via RF

RPM via RF

RPM via RF

I am currently kicking around a way to  reliably transmit engine RPM over an inexpensive low power RF link.

The purpose here is to get rid of the physical cable connection between the sensor and
gauge. In this application the cable is the weak link. If the cost per retro-fit (non-list) stayed under appx 300-400 bucks, it would be quite cost effective. Lots of metal in the area and quite a bit of noise. The RPM is non-critical but needs to be realitively stable. I could do a bit of signal filtering at the A/D box. Distance = 150 - 200ft. Sensor Frequency output = 50Hz to appx 4kHz. High Vibration.

Idealy I was planning to use a relativly high voltage (10-60 VAC) mag sensor to drive a n off the shelf transmitter (like those from Abacom and Linx). I don't think there are any 'Current' supply issues after the monitored gear gets moving, although I suspect that I need to also add a charge cap or battery, so I don't miss start up RPM.

If I could keep all of this small enough, I'd give up the start up RPM in deference to size. It would be nice to 'screw' the "radio" dierctly on the back of the sensor.

Wouldn't bother me to fully pot the finished device and plan to replace rather than repair when a failure occurs.

Anyway, just tossing it around at the moment and thought I'd throw it out there.

Willing to listen to any and all ideas, especially given I am not well versed on transmitting analog sensor signals via a local link.



RE: RPM via RF

As long as there is no any electromagnetic interference in the ether/media, and the rpm of the motor can not cause any harm to anything or any one, then it will be just great. The technology is there as you already observed.

RE: RPM via RF


Thanks for the reply. While I am always apprieciative, I was truely hoping for something more specific. Perhaps some specific recommendations on how someone else has or would do the same or similar.

Thanks again,


RE: RPM via RF

RE: RPM via RF

just a dumb idea on a "for the fun of it" basis.
  If this unit is stationary and you have a relatively clear path.
Use a pick thru a small op amp to allow signal amplitude to be trimmed then feed that into a butchered radio tx (say a cheap walkie talkie) \>then use that to tx the signal to the reciever and run the speaker out thru another op amp to buffer that. The signal will be audio at the frequency of the motor.Maybe run it thru a scmidt trigger or such to clean it up back to a sqaure wave.
You now have a frequency signal at your finger tips indicate it how you will.
 50 to4khz is well within the audio spectrum.
The are a number of cheapo tx units fm bugs and such floating around the hobby market. And some one chip type txs at sites like national semiconductor

Want more dumb ideas? just ask me

Regards Don

RE: RPM via RF

jbartos and don01,

Thanks for the input. Jbartos, I've seen your other posts and must say, WOW, you are THE search guy. Wonderful links, all of which I am checking.

Don01, please keep the ideas coming. None are considered stupid. All ideas are considered.

I look forward to anything further you can supply or anyone else.

Thanks again,


RE: RPM via RF

ok I was in a hobby electronics shop the other day and I spotted a cheap book called "more FM bugs" I didn't have a lot of time but you may find it in a shop near you. (or similiar) if you  dont have any luck post me here and I will try to get more data or an website details


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