Plugging in a speedometer correction device

[robk]

I have a K75C sidehack with smaller wheels and would like to correct the speedo/odometer readings in the standard lunchbox. My thoughts about how to do this are as follows:

1) Remove the speedo amplifier board from the lunchbox to a separate external housing and wire it up.
2) Feed the output of the speedo amplifier into a speedo0meter callibration unit such as Yellow Box or other speedometer correction device.
3) Feed the output of the correction device (5-6 Volts square wave ?) into the lunchbox via pin 22 (the normal connection for the speedo sensor)
4) Where the speedo amplifier board used to sit, jumper input/output pins BE to BA, passing the 5-6 Volts(?) square wave signal straight through to the speedometer/odometer board.

I would very much like to know more about the waveform and voltage output of the speed amplifier board. (Moto Meter 5 4401 173 00)
There is no ABS or other device on the bike which depends on wheel speed so I see no problem there.
I think I'd be OK in sending a stronger amplified signal over the same wiring path as the original weaker signal from the Hall sensor.

Any and all comments very much welcome.

[frankenduck]

https://www.healtech-electronics.com/products/sh/

[frankenduck]

Note that although they run off of the same signal. the speedo and odo are separate circuits. From the factory the odo is usually pretty accurate and the speedo runs about 10% fast.

You can make the speedo read higher or lower:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/speedocal/speedocal.htm

[robk]

I'm aware of the pot to adjust the speedometer but this doesn't fix the odometer.
I'm also aware of several pulse adjustment devices which could fix both the speedometer and odometer.

The problem is that the hall sensor at the final drive is a 2 wire device which does not produce enough voltage for a pulse adjuster to work with.
The amplifier board in the lunchbox boosts this signal up so that the speedometer/odometer board can then work with it.

To hook in a pulse adjuster between the amplifier and the speedo board, it seems to me that the simplest way to do this would be to remove the amplifier from the lunch box, hook it to the pulse adjuster and then feed the amplified and pulse adjusted signal into the lunchbox using the same wire (pin 22).
Inside the lunchbox, I could take the modified signal straight to the speedometer board just by jumpering the pins which used to run in and out of the amplifier
In order to know if this is feasable, I would very much like to know more about the waveform and voltage output of the speedo amplifier board. (Moto Meter 5 4401 173 00).

See the following article for more discussion of boards and signals
https://www.motobrick.com/index.php/topic,8017.msg59081.html#msg59081

[robk]

Another extremely helpful article:

https://www.k100-forum.com/t12022-how-to-get-a-cheap-ebay-speedo-to-work

[The Mighty Gryphon]

I calibrated my speedometers the hard way.  I put the app on my laptop and made a cable by soldering two wires to a 1/8" plug.  I put the wires in the connector on the harness and plug the cable into my laptop.  I use the app to send speed signals to the speedometer.  Remove the speedo, make an adjustment and try again. 

I have found that the correct calibration is pretty much all the way at the stop of the adjustment pot.

If you don't have the app, you can use a soldering gun's magnetic field or wrap some wire around a nail and connect it to a small doorbell transformer.  THen hold it near the pick after you remove it from the final drive.  With North American 60 hertz current the speedometer should indicate about 42 mph.