B E A M - R o b o t i c s
Biology - Electronics - Aesthetics - Mechanics
This design may be used for personal, non-commercial use. If you want to use this in a commercial package in any form then contact the author first.
Copyright A.A. van Zoelen
All rights reserved
I needed a H-bridge design but i didn't had much room on my PCB. The motors that i needed to driven where low current [25 mA] motors. I could use some of the specialised chip designs such as the LM293 but they are costly and they have to much voltage losses. Especially for BEAM robotics purpose. The Tilden H-Bridge is also available but in this case it would be to many components. This idea uses only one chip, has direction control and an enable/disable option. This H-bridge is capable to drive a 25 mA motor in forward and backward direction. One chip can drive up to two motors.
Later tests preformed by Mark Tilden revealed that the chip is capable of driving motors up to 300mA for atleast 60 hours continuously!
ASCII GraphicsIC Type 74S139 or 74F139 ^ ^ The LS type is not suitable. +---------- Reverse Motor | +------- Forward GND | | | | +---- Engage (connected to GND = YES) | | | | | | | | .-+--+--+--+--+--+--+--+-. | 8 7 6 5 4 3 2 1 | | [| | 9 10 11 12 13 14 15 16 | `-+--+--+--+--+--+--+--+-' | | | | | | | | | | | | | Vcc Motor | | +------- Engage | +---------- Forward +------------- Reverse
And the comments of Mark Tilden at the Beam mailing list where:
AA van Zoelen wrote
You can drop all off the transistors and resistors if your motors doesn't drain to much current. You only need a 74F139 or 74S139 NOT the LS version. The chip can provide peak currents up to 100mA for a short time ( < 1sec. ) and to one output at a time. This is for normal connections. I don't know how far you can go with this misbehavior.
Its nothing special but i get the idea how its done.
Mark Tilden answered
It is something special. It involves minimality, expandability, elegance, and a horrible, dangerous violation of the original purposes of the chip.
It's a biomech beaut. I think we should call it the Zoelen Bridge and, with permission, would like to enter it into the lexicon.
The problem with the Z-bridge is that it's standby power (10 - 40 mA for the F and S TTL series) is considerable for solar designs, so it restricts it primarily to battery powered robots. However, it is highly likely that the more efficient 74ACT139 version of this chip can drive and withstand significantly higher inductive loads, and as the 139 is stackable and symettric, all input and output leads can be folded over from one side of the chip to the other to increase the power capacity. This means the Z-bridge can be glued right on the motor itself with minimal modification, reducing lead losses and increasing design flexibility.
As well, the leftover outputs can be used to drive "motor-active" LEDs right on the chip without current drains on the microcore outputs, giving necessary process status during microcore convergence.
A futher advantage is that by using diodes from the four motor drive outputs with paralleled select inputs, permutations on enable states will give different current drive levels. This means trivial and cheap digitally selectable speed control using as many stacked 139s as you want.
Inexpensive small motor drive with enable, short protection and cascadeable control in a commonly available 16DIP package. Very nice indeed, and I can't believe I've been looking at it for years and never made the connection.
Copyright © 1998, A.A. van Zoelen. All rights reserved.
A.A. van Zoelen / email@example.com
Updated: 26 Oct. 1999