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Motor Speed Sensor.

Discussion in 'Sensors and Actuators' started by onesys01, Sep 6, 2018.

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  1. onesys01


    Sep 6, 2018
    Simplified.JPG Schematic.JPG So I am reaching out to all you geniuses here. First of all I am so thankful I was able to find this site because I am at my wits end! The goal of the circuit below is multi faceted.
    • It uses digital relays to switch back and forth from a manual control mode to a control mode run by software. This is the thre ic's at the bottom and that works very nicely.
    • LLC is an Allegro Micro 1425 hall effect sensor, used in automotive speed detection implementations. It has two modes, one is that it can count the number of teeth of a ferritic gear as it passes by and the other mode(which is how I am using it, is to detect a single magnetic field as a permanent magnet rolls around on an armature.
    • The 4013BEJ is a D type flip flop. It's purpose is to divide the signal from the sensor by 2 and to also produce a nice 50% duty cycle of off and on. This signal is then passed into a Numato GPIO board which drives the associated software. The software itself works beautifully and is well understood. Everything else on the circuit is to support these functions.
    • There is a power LED
    • There is a signal LED.
    • There used to be circuity for an under speed, overspeed and halted alarms
    • There used to be circuitry intended to drive a stack-pole for visual indication of current use.
    • It is driven with 12VDC which is divided at various places to get specific voltages where they are needed.
    Here is the problem when I breadboard this circuit it seems to work exactly as intended, when I build a board and put it on together, I don't see the flip flop signal. I am looking for ideas suggestions and someone to mentor me a bit with this issue.
  2. kellys_eye


    Jun 25, 2010
    not so much...

    Clearly this is a 'construction' issue, not an electronic one. Double check your layout and construction techniques.
  3. onesys01


    Sep 6, 2018
    Thank you and that's what I thought too, but the board was professionally produced and has had it's traces tested. Something has to be wrong with my design, no? Board.PNG
  4. kellys_eye


    Jun 25, 2010
    I'm not about to decipher the track layout! but there MUST have been an error between the translation between design and final product.

    I don't see any trace for the GND to the 4013 or the -ve end of C1......

    Oh... and sack the board designers...... damn... that's bad....
  5. onesys01


    Sep 6, 2018
    Possibly, I will have to one by one confirm connectivity of every single pin. This is my first serious paid project and I am pulling my hair out. I won't admit to the reversal of one of the LED's though, that never happened, (except it did). What I fear is I designed it on the computer, then breadboarded it wrong, and somehow it works there and I am not seeing my mistakes, sort of a tail wagging the dog situation. I appreciate you man, you've been very helpful.
  6. onesys01


    Sep 6, 2018
    I'd have to sack myself, the ground is on a ground plane. Just confirmed connectivity.


    May 20, 2017
    Shouldn't pin 6 of the 4013 in the second schematic be connected to ground?
  8. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    When doing computer-aided design for electronic printed circuit board production, it is extremely important that the schematic capture process be exactly reflected in the netlist used to produce the board layout. And vice versa, so if any manual changes in routing are made, those changes are immediately propagated backwards into the schematic. A good PCB software design package will go a long way toward ensuring the process from schematic capture to component placement to routing is done correctly. BTW, the routing on your PCB really sucks.

    What software did your "professionally produced" circuit board designer use? Was a printed schematic made and compared to the schematic you used to produce the breadboard prototype? What design rules were established, followed, and checked before the board was fabricated?

    The devil is in the details when going from the virtual computer-designed and simulated world to the real components world. Simple things, like forgetting (or not knowing) to include bypass capacitors at the power pins of every integrated circuit can quickly torpedo a project and make troubleshooting a nightmare. Your schematic shows several pins of the CD4013 CMOS dual D-type flip-flop unconnected. Although perhaps they are connected to the ground plane of the circuit board, this connection is not documented on the schematic.

    It is verboten to leave unused input pins unconnected or floating on CMOS ICs. ALL unused inputs must be terminated at either Vcc or GND. Please read Section 10 of this Texas Instruments datasheet. Actually, you should read and understand the entire datasheet.

    If you breadboard a circuit from a schematic using a solderless breadboard, and it works properly, then it should also work properly when implemented as a printed circuit board... provided the circuit doesn't depend on uncontrollable things like logic propagation delays, race conditions, stray capacitance and similar anomalies to operate "properly" and fortuitously.

    I like bread-boarding prototypes before making a PCB commitment, but I am fully aware of the problems that can (and do) occur: intermittent or unreliable connections, excessive stray capacitance and/or inductance (especially at high frequencies), inability to handle high currents (especially pulsed high currents), and plain old errors of omission and substitution in making point-to-point connections to components.

    If you continue with your "hands on" journey learning practical electronics you will discover many more "gotchas" that can waste hours, days, even weeks of your time. Best to write these down in a journal of discovery until they are etched deep into your subconscious, lest you keep on repeating them. My favorite: always make sure electrical power of proper voltage and current capacity is available and applied to your breadboard circuit before assuming anything else is amiss. Don't ask how I spent a whole day at the bench in the previous century learning this particular lesson.
    darren adcock and kellys_eye like this.
  9. Minder


    Apr 24, 2015
    If you have the schematic correct, and developed in a PCB software (e.g. Free Kicad) to layout the traces then it will throw up an error if any traces are missing/wrong etc.
    If you just hand layed the traces or sent wrong gerbers, then the professional board producers don't know if you sent it wrong.
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