With this Revision 1 of my original H-Bridge design I decided to use point to point wiring on a piece of perfboard instead of etching my own PC Board. I was also experimenting with making project boxes with heavier 1/4" plastic rather than the 1/8" stuff that surrounds monitors and computer cases. The clear plastic is cool because you can see inside and it no longer feels so much like a black box doing its thing magically; one can see lights flashing inside or possibly smoky looking parts that have been toasted. The plastic that is 1/4" thick is quite hard to bend, check out my tips and experiments with building things with recycled plastic. Thus you can see it looks quite catawompus on one side.

Note that I have used large heat sinks for the driver MOSFETS. I didn't make a front panel for this particular project, but opted to put the manual controls and indicators right on the perfboard.

Oh oh, six DIP IC's. Compare this to my original design which has only 1 DIP IC and a couple of transistors. This may just me and my love of logic, but read on and make your own judgment. I added a fuse for protection for the supply line to the Motor. I also added a jumper so you can run the motor off of either +12 Volts pr +24 Volts. As I stated before I needed bigger heat sinks for the driver MOSFETS. I added 4 led's to show each MOSFET turning on, this was simply to make for easy troubleshooting, in case one of the driver MOSFETS gets burned I will know which one to change. It all fits nicely into a box I made from recycled monitor plastic.

At the top is a 7805 for logic power Vc 5Volts.

This is the layout for the back panel tag board. Notice the power inputs are for +12 Volts and +24 Volts. Two +12Volts batteries in series was the the arrangement I used to supply power to the motors and control board. Left and RIGHT are digital logic signals.
A low will make the motor turn on and go in one or the other direction, in this case it is LEFT and RIGHT for my Side Hill Gouger. The Motor + and Motor - are the power wires to the DC Motor. the timing wheel signal was something I was thinking about using but never did.

The +5 Volts Vcc was for any external power I needed somewhere else so I wouldn't have to wire up another regulator.


Notice the Molex connector used for the power and to run the motor. I like to make my project boxes portable so I can simply unplug it and move it on to another project. The digital signals are sent out via a 9 pin DB connector which I have also collected lots of. If I need more pins I can use DB-25 connectors which I have also collected lots of.

This block diagram shows the key componets A-B-C-D are the 2 N-Type MOSFETS and the two P-type MOSFETS in a true H type arrangement. Each MOSFET has a dual colled LED attached to it so I can see which ones are on or off. It aids me a lot in case something goes wrong as I can see exactly which MOSFET may have been burned. So in operation (A) and (C) will turn on for one direction then (B) and (D) will turn on for the other direction. Note the jumper selector to select +12V or +24V. This jumper only selects power to the Motor. The +12 Volts coming at (H) goes directly to the regulator to run the batch of logic IC's in the centre of the Control Board. The fuse is only for the Motor voltage thus if the fuse blows the logic will still operate. LEDS will still flash but the motor won't turn on because it has no power. The front panel is shown on the right side with the two PB switches and LED indicators for directions and +5 Volts Vcc. The rear panel is shown on the left side of the diagram for Power Input, DC Motor Drive and digital inputs at TTL levels. On this particular diagram I have forgot to label the two digital inputs.


In this diagram I wanted to show the logical way to run the power to the driver MOSFETS. (A) and (D) are N-Type MOSFETS so they need ground on the SOURCE terminal. They are both vertical to each other.So one wire puts in the grounds needed. (B) and (C) are both P-Type MOSFETS and need the + MOTOR DRIVE VOLTAGE (+12V or +24V) on their source terminal. These two are vertical to each other so one more wire gives them the + voltage they need from the fuse. The top two (A) and (B) need their DRAIN terminals tied together and go to one side of the MOTOR drive line. Similarily the (C) and (D) need their DRAIN terminals tied together and got to the other side of the MOTOR drive line. With this method of thinking you are left with four digital lines from that block of IC's to turn on the MOSFETS. So 4 more wires and you are all done the wiring. Ha!

In this schematic you will see the 4 wires you need to go to the GATES of the MOSFET drivers. They are appropriately named (A)-(B)-(C)-(D). (B) is a P-Mosfet and as such needs a low to turn on. (D) is a N-Mosfet and needs a high to turn on. the same scheme is used for (A) and (C).

I will attempt to simplify the usage of all those gates you see in the schematic. I used a 7406 open collector inverter to level shift the logic level to the DC motor drive level. The logic runs at +5Volts Vcc yet the motor runs at at +12 Volts or +24 Volts. I wanted the MOSFETS to turn on or off with the levels of voltage that was being used by the motor. Thus the 7406 with its four 10K pullups does this job. I used up all 6 of the 7406 gates. You can see to turn on the (B) MOSFET I needed a low and the logic from nand gate 2 was a low, so I had to pass it straight through. I used one of the spare gates from the 7506 to do this. A similar situation occured for the gate signal on the (C) MOSFET.

So that takes care of six gates of IC5 the 7406 inverter. And it also uses 4 resistors.

Another bulk of the schematic is taken up with those LED indicators. There is a total of 6 LED indicators. Of these (4) are dual colored leds and need an inverter so one color or the other is shown sepending on the logic level present. Thus 4 gates of IC-6 are used for this purpose. The other two LED indicators are used for the front panel to what direction the motor is turning in. this uses up two spare gates from IC6 and IC2. In conclusion the LED indicators have used up all the gates of IC6 and 2 gates from IC2 the NAND gate. They also required 6 resistors.

The bulk of the work is done by the two NAND gates IC1 AND IC2. They handle the three signals REV, GO AND FWD. If GO is HIGH and REV is HIGH (B)-(D) MOSFETS will turn on. Similarly if GO is HIGH and FWD is HIGH (A)- (C) MOSFETS will turn on. The reason for the GO signal is that I didn't want any of the MOSFETS to be turned on unless a button is pushed appropriately or a proper computer signal arrives. Compare this to my original design where I had to use big power transistors to turn off/on the whole power line to the motor.

To explain the last gates we shall start at the input side of the schematic. If the computer or the REV PB switch produces a LOW, REV goes HIGH active via the inverter and tries to move the motor in that direction. But the motor can't go unless it gets a HIGH active GO signal. A similar operation will happen with the FWD PB switch and computer input and the motor won't go again unless it has that active HIGH GO signal.

The GO signal will try to go HIGH if either input goes LOW. The XOR gate makes sure both both inputs are not LOW. If those conditions are met the GO signal goes HIGH and the motor is allowed to turn on in either the FWD or REV direction. This may seem like overkill as you say you would never try to push both buttons at once. That would require two hands or awful big fingers. But the thing is that I want to control the motor from a computer. It is easy to make a mistake when one is coding, all one has to do is forget to reset 1 bit of data. In this case your computer program would wipe out your motor driver very quickly.

So I have used up 6 TTL gate packages with only 3 spare XOR gates and 3 spare inverter gates. The use was 2-7400 nand gates, 1-7406 open collector inverter, 1-7486 XOR, and 2-7404 inverter. It adds up real quick.

The justification for using so many IC's other than my tendancy to use logic gates when I see on's and off's is as follows. If you are going to wire up a circuit with one IC socket it is not much extra work to wire in a few more if you have the real estate available on the board. A real bonus on a good circuit board is to have lots of LED indicators to show what is going on. This circuit used lots of indicators for this purpose. A extra extra plus of a good designed board is protection from operator error power surges overuse etc. In this case I was going to make it computer interface friendly. If the computer ever told the motor to turn left and right at the same time the board would have been toast for sure. The fuse was there and might have protected the circuit. But fuses are slow compared to digital logic. So in essence I have double protected the control board from errors.

All in all I like the design and it functions great. But there are always improvements so see my Rev-2 design for some more improvements.

Revised 2013 by Larry Gentleman