Train Tachometer Interface box help!

Discussion in 'The Projects Forum' started by João Paulo, Jul 14, 2015.

  1. João Paulo

    Thread Starter New Member

    Jul 14, 2015
    Hard Summer Project!!

    What have I got into? Hahaha :D Basically I have to build instrumentation to sense position and signal of a train tachometer sensor and display position and speed on LCD. The problem is I have almost none background on eletronics but I am willing to learn the maximum I can and I hope you could help!

    Here are the specifications:

    Below please find the spec of the tachometer interface box,

    speed calculation position calculation relative & abs
    seven segment LED to display position (comedy size)
    position display on LCD
    serial interface in/out to PC using FTDI lead
    isolated zero volt output for channel A/B (operate up to 30 V, check)
    three LEDS to indicate speed units (m/s, km/h, mph)
    push button to reset relative distance
    input/output immune up to maximum rating 60V
    supply for the tachometer 12V (check)
    switch for the supply
    ERROR detection for QA/QB
    Maximum speed of train 50 km/h

    For the project I have to choose the PIC, which I am left into darkness. And also I have to read some backgrounds in quadrature encoders, signal conditioning, pic programming(change notification interrupt and input capture module, etc).

    I really wanna learn about it and also make a good project( and impression) and that's why I'm gathering as much help as I can!

    Any questions please ask!
  2. crutschow


    Mar 14, 2008
    What is the nature of the tachometer signal you are trying to monitor?
    You need to display both speed and position from this one signal?
    What does "isolated zero volt output for channel A/B (operate up to 30 V, check)" mean?
    Need more info to help you.
  3. João Paulo

    Thread Starter New Member

    Jul 14, 2015

    Yeah, actually there are two channels one is shifted by 90 degrees from other, they serve to inform if the rotation is clockwise or counterclockwise, but I'm going to use only one of them, once I just need the absolute position.

    From what I undestood I need to isolate the signal for safe work with the pic, I have to use a optoisolator in order to do that.
  4. MaxHeadRoom


    Jul 18, 2013
    If you want to do this with a pic, and certainly they have the capability, it is quite a comprehensive starter project for a newbee, particularly with no electronic experience.
    The PIC has a function known as CCP Capture/Compare/PWM, some have several of these, the Capture can be used to to detect not only rpm but direction from the 90° quadrature pulses, you would not require high resolution for this.
    The timer used by the Capture input can use a 38Khz clock crystal to aid in the accurate timing.
    You would also have to decide on the programming language C or Assembly, you also would need a Pic programmer of some kind.
    Why is isolation required, especially on a vehicle?.
    If you have all summer you may make it!;)