H-Bridge Schematic

As indicated on Puck’s blog we have been talking about a controller board to drive the four motors on the Rover.  The original circuit used an op-amp to convert the 3.3V signal from the Rabbit processor to the 5V signal required by the H-Bridges.  The main reason for using the op-amp was quite pragmatic – I had them on hand.  The new circuit uses a bus driver, 74HCT541, instead.  The inputs on the 74HCT541 are TTL  compatible, that is the meaning  of the “T” in the device name, so they will easily handle the 3.3V signals from the Rabbit.  You can download all the DipTrace design files from here (about 300kB).

As can be seen from the schematic, it has the following features:

1. Two 50-pin headers which allow the board to be inserted anywhere in the “stack” of Rabbit MiniCore boards.
2. A socket for an XBee module if/when we want to try using one in place of the RCM5600W (WiFi).
3. A power supply which has both +5V and +3.3V.  The +5 is for the ‘541 as well as the MiniCore.  The +3.3 is for the XBee (if used)
4. A 74HCT541 to translate the +3.3V logic levels of the Rabbit to the +5V required by the H-Bridges
5. Four H-Bridges, one for each motor.  See my earlier post and this post on Puck’s blog.
6. A 12 terminal block with screw terminals for all the connections – power input, +5V for the RCM5600W and the drive signals for the H-Bridges

Here are some photos of the circuit boards.  The hand-wired board was used to test the initial library and to determine some of the motor characteristics.  The printed circuit board will be used in the final product.  I used DipTrace to do the schematic and board layout.  DipTrace generated the Gerber files which are needed to make the PCBs.  The PCBs were etched by Alberta Printed Circuits.  The cost for the two boards, including the silk screen, was $94. and about $15 for shipping via FedEx.  I have used APC a number of times in the past and they have always provided excellent service.

Hand-wired board

Printed Circuit Boards