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750c Display Documentation

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  • AZguy
    commented on 's reply
    Well the battery voltage goes up there to be able to turn the controller on... think of it this way - if all they did was send 5V to the display to turn it on then there would be no 5V to turn it on - catch 22!... so they send the "raw" battery voltage and that's the signal that gets sent back via the pushbutton to turn it on. It's already up there so pretty much most any microcontroller will have an A/D to measure it... but unfortunately best case the components are going to be 1% tolerance and the converter accurate to 6-8LSB so accuracy isn't likely going to be that good - one reason we likely see bars far more often than numbers.

    The controller measures battery current in order to limit the PAS levels, etc. so that is what I suspect gets sent up digitally

    OTOH it wouldn't be hard to use ground to the pushbutton to turn things on but definitely not as easy as using the battery + ... oh well...

  • 73Eldo
    commented on 's reply
    I didn't know they did that. Doesn't seem like it would be the best way to do it but I guess when a lot of its copies of copies and translated from translations you can end up with just about anything.

  • AZguy
    commented on 's reply
    FWIW with BBSxx the battery voltage does a pass through to the display and the display measures it (at least mine does) for the readout... When I last hacked the communication protocol I didn't find voltage being passed as a parameter but it's been quite a while since I looked and my brain is old and feeble.... there were some parameters I couldn't figure out too... current (or power?) was a different matter and there was a parameter sent that varied with motor output - I had no way to scale it so not sure whether it was current or power although if I spent enough time likely could figger it out...

  • 73Eldo
    commented on 's reply
    There isn't a direct connection between the battery and display. The controller is where the battery voltage is being 'read' and that information is then part of the data stream that is available for the display to display if its programmed to do so. They in theory are reading actual battery voltage. I think where the confusion may be is that a '72 volt' lithium battery isn't always 72 volts. The named voltage is usually based on the nominal per cell voltage of 3.6 or 3.7 but at 100% charge would be 4.2. So a 72v pack is likely 20 3.6v nominal volt cells. If you do a 100% charge to 4.2 each cell thats 84 volts.

    What I was talking about above is many displays have a percent or empty full sort of display so they need to know the voltage so that graph is reasonably accurate.

  • Andrewol
    commented on 's reply
    What is the reason of this display showing high overvoltage than actual battery voltage?

  • Andrewol
    commented on 's reply
    Hi. Do you know why this display has high overvoltage reading, over 6V than actual value?

  • paxtana
    commented on 's reply
    750c does not have bluetooth and I never heard of that controller; generally speaking displays are not compatible with other random controllers as they use varying communication protocols

  • creativeusername25
    replied
    Hello,

    So I am trying to connect my 750c to my FarDriver 72360 controller and I was wondering if anyone had an idea how to do that given the parameters in the Bluetooth app (I’ll attach a picture). The controller has transmit and receive wires coming out of it that go to the Bluetooth receiver, and also has a digital speed pulse wire. Any help would be appreciated!

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  • eRider
    commented on 's reply
    Oh ok, thanks

  • AZguy
    commented on 's reply
    The displays just put out what the controller is reporting and it's poor resolution, update speed, etc. makes them almost pointless

    There are third party units where a shunt is installed inline upstream of the motor that give very good numbers and some will log and do amp-hour/watt-hour totalizers... much better solution if the data is important to you

  • eRider
    replied
    My DPC-18 display died so I bought a 750c because it displays the watts nicely. However when I ride at a steady power, I noticed the watts display jumping between two values about 50 watts apart. When I select PAS of 100%, the power reads 1.5 kW, which is ok for full scale. But when I select PAS level 10%, I get flicking between 112 or 168 watts, which is not ok at that end of the scale. I expected a much more accurate indication of my power.

    So I switched to current and found that the current display resolution is in whole amps! Anyone else noticed this? The 112 and the 168 is either 2 amps or 3 amps times the battery voltage. So they just multiply the whole amps by the battery voltage to get the watts. That's really poor software engineering. Current should have had a resolution of 100 mA or better. Then it's just a matter of correct filtering to get a steady but accurate readout of either current or power.
    Last edited by eRider; 06-30-2023, 03:38 PM.

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  • Pauli gualtieri
    commented on 's reply
    I already tried but it doesn't work

  • brothergc
    replied
    Originally posted by Pauli gualtieri View Post
    The 1919 lock code on my display 750c doesnt work why?
    Try code 1199

    Leave a comment:


  • Pauli gualtieri
    replied
    The 1919 lock code on my display 750c doesnt work why?

    Leave a comment:


  • BenTen
    replied
    Hi, hopefully this information is useful for everybody.

    I have found 2 different simple methods of extracting the pin/password from the 750c in case of lost or forgotten situations.

    My friend forgot his pin and asked me to help retrieve it.

    Open the display using the directions in the thread so you have access to the PCB.

    There should be a small 8 legged eeprom chip next to the stm32 MCU.
    The eeprom should be labeled 24LC04.

    You have 2 options depending on your ability to solder.

    Option 1 is to de-solder the chip and read the data with a chip reader (see amazon pic below)
    You will need to set the data to Big-endian, the pin code can be seen in the screenshot below.

    It shows 1A 30. When you convert these bits to decimal, you get 26 48. The bits should be converted separately.

    The 2nd option is to use a cheap logic analyzer (see amazon below)

    You need to attach the clips to pins 6 and 5 of the eeprom (SDA, SCL) and GND

    A 24v power supply also needs to be connected

    I won't go into how to setup the logic analyzer software, there is plenty of tutorial on YouTube. You need to setup an I2C protocol.

    Once set up, start the analyzer and turn on the display. You will see a short burst of data.

    Filter the results to show only data and the pin will be displayed in the same hex format (as circled)
    The write section refers to the location in the eeprom (7E 7D 7F)
    the read lines refers to the useful data
    So you only need to look for the data at 0x7E and 0x7F

    1A 30

    Convert the bits to decimal and you have your pin.
    Attached Files
    Last edited by BenTen; 04-27-2023, 07:16 AM.

    Leave a comment:

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