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    The Builders->Member Projects: Scrap Books->Mike J. Robot #2 Journal->10/26/2004  

Mike J. ( B9-0002 )

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10/26/2004 - Interfacing the Motors, Sensors & Soil Sampler to the OOPic II

Overview Photo showing the completed interface for the Leg Section


The nine wires coming from each Motor as well as the Soil Sampler must be interfaced to the OOPics.  

This involves two circuit boards, one purchased off the shelf and another which I designed and had produced for me.

The first is the Magnevation Dual PMW Driver Board which I purchased.  This printed circuit board (PCB) allows the OOPic to control two DC motors.  It has inputs for ground and the motor voltage (24vDC in my case) and outputs two wires for each motor.  It is made to work with the OOPic and the two are connected together via their 40 pin connectors using a short ribbon cable.

Our other 7 wires (S1, S2, S3, L1, L2, +5vDC, GND) feed out of a custom designed PCB which I created using the service provided by www.ExpressPCB.com
This Encoder Interface Board (EIB) provides a spot for the resistors and transistors needed to allow the OOPic to power (L1, L2, GND, +5vDC) and read the Encoder outputs (S1, S2) and the optical switch output (S3).

Here's a photo of my Encoder Interface Board with components:

Here are the EIB's circuit diagram and the board layout files. Note that you'll need the free ExpressPCB software to open these!

EIB Circuit Diagram
EIB Board Layout

Here's a shot of the EIB after build up:


And Here it is attached to the Magnevation Dual PWM board.


Molex terminals crimped and soldered.


Optical Switches

I'm using a H21A1/2/3 Slotted Optical switch.  This device has four pins (1-4).  Pins 2&4 go to Ground, Pin 1 connects to L1 & Pin 3 is the output which connects to S3.
Here's the data sheet for this switch (pdf).  These can be purchased from DigiKey. (DigiKey part # H21A1-ND, $1.08 each)

Between the EIB and the Magnevation Dual PWM we have completely interfaced both of the 9-pin motor connectors (both the Hip Actuator motor and the Torso Rotation motor).


Soil Sampler Control

That leaves the Soil Sampler interface as the last responsibility of the leg section OOPic.

I had planned to use relays but decided it would be best if I could come up with a solid state circuit that the OOPic could use to control the Soil Sampler.
I also wanted to be able to stop the Soil Sampler in mid-motion when the Power Pack is pulled.  So I bring both the SS's ground supply wire and it's trigger wire up to the OOPic using a two wire cable.  Black(SS1) is the SS's ground line (cut this and everything stops, ie Power Pack pulled).  Purple(SS2) is the SS's Trigger line (hold this to ground for about three seconds to start the cycle).

I didn't make a PCB for this. Instead I soldered everything together in-line and used wire shrink tube to protect it.   Basically there are two circuits, SS1 & SS2, each of which can connect it's output line to ground under OOPic Control.  The OOPic will control the Soil Sampler by grounding SS1 (cycle power) for 20 seconds (long enough to cycle) and SS2 (trigger ground) for about three seconds.  If the power pack is pulled then SS1 can be opened and the Soil Sampler will stop moving until SS2 is closed again (Power pack plugged back in).  

I used some transistors from Radio Shack to construct the solid state relays.
Here's the circuit I used:

(Click here to Download the ExpressPCB Circuit File)


Power Bus and OOPic Power connections

I'm using 16 gauge AC power cords to bus DC power through the Robot.  They are readily available, flexible, and can be purchased with connectors on each end.

The ones I am using are three wire conductors.  I'm using Green as Ground, Blue as 12vDC and Brown as 24vDC.  A patch cord with a sliced in feed for the leg section circuits is used in the leg section:


OOPic I/O Line Usage

Every sensor(input) and every output from the OOPic needs a dedicated I/O line.  Here's a list of the I/O lines used and their connection.  

I/O Line 1:  SS1 - Active Low Output. Connects the Soil Sampler's Ground line.
I/O Line 2:  SS2 - Active Low Output. Triggers the Soil Sampler cycle when held low for three seconds.

I/O Lines 18, 24 & 26 - PWM outputs for motor 1 (Hip actuator).
I/O Lines 17, 25 & 27 - PWM outputs for motor 2 (Torso Rotation).

I/O Lines 15 & 14- Motor 1 (hip) Encoder inputs (S1, S2).
I/O Lines 13 Motor 1 (hip) Optical switch input (S3)

I/O Lines 10 & 11- Motor 2 (torso) Encoder inputs (S1, S2).
I/O Lines 12 Motor 2 (torso) Optical switch input (S3)


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