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Firstly, I have no electronic experience, so I don't know if the below is practical, or what hardware and software would be required to make it happen.

Basically I would like to transmit the value shown on a basic digital measuring wheel, in real time, to an Android phone. It doesn't matter if this is via a USB cable, Bluetooth or another technology. I realise I would need to write the Android application to receive and process the measurement, but for now I am questioning the possibility of accessing, processing and transmitting the data. I suppose my questions are:

  1. Is it likely that I will be able to access the measuring device display's value in some meaningful format that I can work with?
  2. How likely is it that I - an electronic layman - will be able to figure out how to undertake such a task with some research and the good people of Stack Exchange?
  3. How might I go about point 2 (and with what software and hardware)?

The measuring wheel would be something like this

I realise that anyone answering these questions will be making some assumptions about the technologies inside the display, so if you could indicate the confidence in such assumptions then that would be great.

enter image description here

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  • \$\begingroup\$ forget about usb cables, Bluetooth and about android for now ... you have to be able to use a microcontroller to read data from the wheel first ... all the rest of your project cannot happen until you succeed in reading the data \$\endgroup\$
    – jsotola
    Commented Oct 21, 2022 at 16:33
  • \$\begingroup\$ Are you wanting to make your own wheel? Adapt an existing cheap one? Find an interfacable professional one? All are perfectly feasible, it comes down to what you're good at. \$\endgroup\$
    – jonathanjo
    Commented Oct 21, 2022 at 16:34
  • \$\begingroup\$ It is frustrating when you know that the displayed digits are inaccessibly stored inside a microcontroller chip. It is possible to capture digital signals transferred between this microcontroller and the 6-digit LCD display, but there are quite a few digital signals that must be captured, and they are likely encoded with complex pulse timing - it is not a simple decoding process....(continued).... \$\endgroup\$
    – glen_geek
    Commented Oct 21, 2022 at 16:49
  • \$\begingroup\$ I'm hoping to buy a cheap wheel and adapt that. I have an analogue (purely mechanical) wheel at the moment that I use for work, but I'm assuming it would be harder to adapt that to digitise and transmit data than to transmit data from a digital wheel. I don't want to buy a fancy wheel, as the project actually relates to the software I will build and a bunch of other stuff, however, getting a live measurement to the phone is necessary for a variety of reasons. I basically just need to get a wheeled chainage. A simple digital cycle computer could be used if that was easier to get data from? \$\endgroup\$
    – TameAim
    Commented Oct 21, 2022 at 16:54
  • \$\begingroup\$ Another approach captures signals between the wheel sensor and microcontroller. There will be fewer signals to capture - these signals are likely digital or nearly digital. Then you must count pulses and scale that count to represent distance - a job for a microcontroller (whose programming learning-curve is substantial). \$\endgroup\$
    – glen_geek
    Commented Oct 21, 2022 at 16:55

3 Answers 3

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Sorry if I sound negative when I answer to your questions.

But just a note that you ask how easy it would be to interface to the display of the device. It would be much simpler to either try to interface to some other part of the device than the display, or replace the innards with some Bluetooth enabled MCU board, and just use the wheel sensor to count distance.

  1. If you have to ask, it is extremly unlikely. It is likely not worth doing for an electronics professional either. Unless the manual says there is some interface you can get readings. The display is just LCD glass, the display driving signals are just square waves and may be multiplexed. It may be worth to do something else, like replacing the electronics, or buy another kind of wheel which already communicates with phones.

  2. Based on what I wrote to first question, you really don't want to interface to the display. Or if you do want to use the display, have some processor with camera analyzing the display contents and converting it into whatever text or numbers you want to send to phone.

  3. Learning to do the project one little step at a time. One piece of hardware working at a time, one line of software working at a time.

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  • \$\begingroup\$ Thanks everyone for your replies. I can see this route would be beyond me, as I really do have little understanding of electronics. How about this... Presumably each time the magnet on a bike wheel passes a wireless cycle computer sensor the sensor sends some signal to the computer. Could I setup a device that senses/intercepts each time the sensor sends a signal (regardless of the signal type). Then, each time it intercepts a signal the new device sends it's own signal for the phone to pickup. On a 1m circumference wheel that would only fire once a turn, but that's probably ok for my needs. \$\endgroup\$
    – TameAim
    Commented Oct 21, 2022 at 17:11
  • \$\begingroup\$ Or, to cut out the sensor entirely, is there an electronic device that can communicate with my phone, which records each time a magnet passes by it. \$\endgroup\$
    – TameAim
    Commented Oct 21, 2022 at 17:13
  • \$\begingroup\$ en.wikipedia.org/wiki/Hall_effect_sensor \$\endgroup\$
    – fizzle
    Commented Oct 21, 2022 at 18:56
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    \$\begingroup\$ @TameAim Perhaps a slightly silly way to interface the wheel would be to wire some sensor to the microphone jack. A small electrical pulse sounds like a click. Then you could write an Android app to count the clicks. This may or may not work together with the wheel's usual display \$\endgroup\$
    – Criticize SE actions means ban
    Commented Oct 21, 2022 at 20:10
  • \$\begingroup\$ @TameAim If you take apart the measuring wheel you can see what's inside it - no need to guess! well, you may take it apart and still not understand what you're looking at, then you can ask here (I think that question would be small enough) \$\endgroup\$
    – Criticize SE actions means ban
    Commented Oct 21, 2022 at 20:12
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The problem has probably already been solved in the bicycle world. Have a look for Cycling Speed Cadence Sensor Bluetooth devices and you should find one that will already have a phone application.

It looks like you have a metre-wheel so it should be just a matter of attaching a magnet to one of the wheel spokes, mounting the sensor / transmitter on the fork and configuring it or the phone app to tell it that the wheel circumference is 1000 mm. You should be able to get "0.000 km" (1 m) resolution on the app.

Alternatively search for Bluetooth Digital Measuring Wheel which will have a readymade solution.

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  • \$\begingroup\$ I now have the hub sensor of a Garmin cadence device in front of me. A shame the crank sensor is nowhere to be found and I fear may be long lost. I shall do some more research, but this certainly seems to be the way to go. Thanks. \$\endgroup\$
    – TameAim
    Commented Oct 21, 2022 at 17:39
  • \$\begingroup\$ This looks much easier than my answer! \$\endgroup\$
    – jonathanjo
    Commented Oct 21, 2022 at 17:47
  • \$\begingroup\$ Certainly solved for the bike world! There's a standard GATT for how the devices interface. Good detailed explanation here learn.adafruit.com/… Basically all you need to do is get a GATT bluetooth cadence sensor (magnet + bluetooth) and then a bike computer or bike computer app that shows the information you need (distance in metres). \$\endgroup\$
    – jonathanjo
    Commented Oct 21, 2022 at 17:54
  • \$\begingroup\$ Been reading about the Bluetooth standard (specifically 4.0) and it looks like I could connect my phone to one of these devices and access the data directly, with some JavaScript in a Chromium based browser. I can't see number of rotations in the documentation HERE, presumably because the sensors don't know when they started. But I'm sure there must be some trigger I can use each time a rotation occurs. I'm ordering a MEILAN C3, for £14.99 it's worth a shot! \$\endgroup\$
    – TameAim
    Commented Oct 21, 2022 at 18:19
  • \$\begingroup\$ Bike sensors seem like a simple solution. BUT most only give one pulse per revolution. If your wheel has 1m circumference, would you be satisfied with +/- 1m resolution? You could attach multiple magnets spread around the rim as @jonathanjo suggests - then do some math to scale-back the displayed result. Another potential problem - some require a few turns to "wake-up". \$\endgroup\$
    – glen_geek
    Commented Oct 21, 2022 at 19:14
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If you want to make/adapt one, and you're a newcomer to electronics, here are some suggestions, which are basically get quadrature off something, get input into phone/computer, do display and calculations there.

The easiest kinds of sensors for this are Hall-effect magnetic sensors with some magnets. You might be able to examine a ready-made digital one like you linked to, which is likely to be very much like I'm describing. But often it's easier to start with something very, very, simple.

  1. Forget interfacing to an existing electronic device
  2. Use "non-latching" Hall effect sensors
  3. On a 5-spoked wheel, use one magnet per spoke (or just one on the wheel)
  4. Use two sensors, arrange to overlap.
  5. Learn about quadrature encoding.
  6. Use an Arduino with USB connection (one with ATmega 32u4)
  7. Make the Arduino act like a USB keyboard which presses "+" or "-" each time a magnet passes.
  8. Do counting on phone app. Perhaps use Kivy

Visually it looks like this:

enter image description here

Things to Read

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