Thursday, 13 February 2014

Interface Bench Test - Part 1

My general plan for testing this interface is to perform a complete bench test outside of the Armdroid enclosure.

Only when I'm happy with everything, will I remove my existing circuit board and make the changes necessary to accommodate either circuit in future.

The picture on the right shows the circuit board remounted on the base plate to help protect everything whilst testing.

My initial inspection check-list included:
  • Check the board for dry joints and re-solder any found
  • Visual inspection - looking for signs of burnt-out components etc.
  • Held the board under a strong light and checked the underside to ensure there no solder bridges between the tracks (as per the instruction manual)

Power Connection

Colne Robotics implemented a modified 4-way socket to ensure correct polarity using a polarising pin.   I crimped up a power supply connector, but didn't bother to protect from incorrect installation.  I will just have to be very careful!

Basically, you need to ensure +15 V is applied to the right most pin (as pictured below), and GND to either of the left-two most pins:

My bench power supply has now been preset to output 15.4V with a maximum current of approximately 3 Amps.

A basic power check was performed to verify the +5V power regulator (7805) is good, and all chips are receiving power.   If you measure the input voltage to the 7805 regulator, this should be approximately 12V after the input voltage has been resisted through R14 (big green thing) which is rated 18ohm 5w :

To check each individual chip is receiving power - check all datasheets and measure with a multimeter by checking the VCC pins have approximately +5V, with the exception of the ULN2003 Darlingtons which should have +15V on their COM ( pin 9 ) connections.

Computer Connection

This is where things are different to my prototype model.   This generation of circuit board uses a 10-way IDC connector, instead of the not-so-good edge style connector.

I made up a small 1-foot length of IDC cabling terminated with female connectors on both ends.

You can clearly see in the photograph above, red stripe indicates pin 1.  Pin numbering of these connectors are easiest described by an illustration:

At the other end - consideration was also given how to breakout the ribbon cabling:

I recently purchased this breakout board from Winford Engineering of Bay City, Michigan, USA.

It's a 2x5 (10-way) 0.1" IDC header breadboard adapter which makes for a perfectly reliable way of connecting Armdroid to Raspberry Pi, Arduino, etc.  As you can see, with an adapter like this, it's quick and easy to test what pin does what using a multimeter/digital logic probe.  Also, the PCB silk-screening makes it very easy to identify the pin-outs for this type of connector.

Anyway, if you happen to order one of these, please do mention my name whilst ordering, John will certainly go out of his way to accommodate you!

Stepper Motor Connection

I've previously talked about the Armdroid's official motoring number goes 1 - 6 left to right.  For the purpose of testing, I have installed a single stepper motor into channel 1 as pictured below:

When we get some idea channel one is working satisfactory, all remaining channels will be tested.

Microswitch Sensors
Not currently being tested - will need to add the optional 74LS366 3-State Buffer (IC5) to enable this feature.   I actually intend to show how you can add these sensors sometime, if your Armdroid is missing them.

Finally, a photograph of the interface ready to start bench testing:

Next, we'll confirm the interface pinout assignments, and soon be in position to connect up the Arduino.