Gas station without pumps

2017 November 27

Power board soldered

Filed under: Robotics — gasstationwithoutpumps @ 13:26
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This morning I managed to fix the problems that I had created for myself by my mistakes in soldering yesterday.  The power board is  now soldered and passes continuity tests (no adjacent pins shorted, all header pins connected where they are supposed to be.

Finished board, with annotation for the header pins. The whole board is 5cm×7cm.

The power board has several functions:

  • The pair of H-bridges for the motors, powered directly from battery power input at the lower left, and controlled by PWM and DIR signals from the Teensy board (header pins at the top). The motor output wires are red and white header pins on the left side of the board, to match the red and white wires on the motors.  The two motors have red and white with opposite M1/M2 connections, so that matching DIR signal drives the motors in opposite directions.  Because the motors are mounted with shafts in opposite directions, this should result in the wheels turning the same way.
    There is a row of header pins on the right (input side) of each H-bridge, for hooking up oscilloscopes or other test equipment.  The EN– signal could be shorted to GND with a shorting plug, but the documentation claims that there is a pull-down resistor internally, so floating should be fine.
    The VM pins of the H-bridges have 220µF electrolytic capacitors as bypass, to reduce PWM noise from propagating back through the battery.  I was planning to add 10µF ceramic capacitors at the Vin pins, to reduce high-frequency noise, but I ran out of room.  If the high-frequency noise is a problem, I can try to squeeze in some bypass capacitors.
  • NCP7805 5V 1A regulator (bottom center).  All the red and black pair to the right of the motor control are 5V and GND.  The GND pin of the regulator is the only place where the 5V and battery power systems are connected.
  • The multiplexer connects one of the 8 white pins on the top right to the “out” pin, controlled by S2, S1, and S0. Up to 8 tape sensors can be connected with standard 3-wire servo cables.
  • The 8 yellow pins are not connected to anything—they are there just to provide alignment for servo cables sending 5V power to other boards.  I may not need any of these connections, as the Teensy board can be powered from the 5V and Gnd connections adjacent to the motor signals and tape-sensor signals.
  • There are also 4 pairs of yellow pins just above and to the right of the regulator.  These are intended for gathering the encoder wires from the two motors and transferring them to a single cable up to the Teensy board.  The power and ground connections there can also be used for the encoders.

This board will have a mass of connectors to it:

  • battery (3-wire servo cable)
  • motor connections (4 separate wires)
  • motor encoder connections  (8 separate wires: +5V, GND, ENC1, and ENC2 for each motor)
  • motor cable from Teensy (4 wires or 6 wires, depending whether 5V and GND included)
  • tape-sensor cable to Teensy (4 wires or 6 wires, depending whether 5V and GND included)
  • encoder cable to Teensy (4 wires)
  • tape-wire sensors (3-wire servo cable to each sensor)

I still have to lay out and solder the carrier board for the Teensy, but that should be relatively easy, as I don’t have nearly so many wires and I only need to populate a few of the connectors.


1 Comment »

  1. […] soldering would be a quick fix, at least until the thin wires broke, but is a bit of a pain, as my power board was crammed rather tight. The PC board is a better long-term option, but I need to look ahead to […]

    Pingback by Robot moving, but unreliably | Gas station without pumps — 2018 January 1 @ 10:06 | Reply

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