identify h-bridge controller inputs

fschutzman · 2011-05-23 17:27

A number of years ago I purchased two h-bridge controller boards on ebay. The other day I was looking at them and I could figure out most of the connections except the inputs. There is a five pin connector on one side of the board with some rather cryptic lettering. I think two of the pins are for pwm inputs but the other three I am not sure of. I have included a picture. The board is using a sn754410ne chip. I tried to follow the foil traces but they do not go directly to the chip. I would like to use the controllers on a small bot with a dc motors. Here is a picture of the board.

Fred

PJAllen · 2011-05-23 17:50

D - Direction
E - Enable
R - Return (Ground?)
?

RobotWorkshop · 2011-05-23 18:18

No way to tell from that picture. Can you get a good picture of the top and bottom of the boards that show some details?? What about the other chips on the board? Does one happen to be a 74HC14 chip? You can google for Handyboard schematics to get a good idea on how that h-bridge chip may be wired. If there is a model # on the board search for that too. Otherwise you'll have to start tracing out the board to confirm the directions. Mr Allen's suggestion is a good place to start.

fschutzman · 2011-05-23 22:32

There isn't any model number or much else on the board. I have two boards, on one of the boards they scratched out the numbers on the chip, on the other they didn't (go figure). There are three chips:
1. sn754410ne which I know is a h-bridge chip.
2. TI cd4093be which according to a spec sheet is a cmos quad 2-input nand schmitt trigger.
3. nec ps2501-4 which according to a spec sheet is a quad opticoupler ( this is what the pins in question are connected to via a resistor array) I am sure this is to isolate the dc voltage on the pins.

I am thinking 1d and 2d are data pins for pwm signals. I am wondering if 1e and 2e are some kind of "enable" pins which have to be high or low to pass a signal. There is an "r" pin which could be a reset switch but why?

I will try to get some better pictures. Thanks for the help so far.

Fred

fschutzman · 2011-05-23 23:26

I do think after looking at a number of schematics of the sn754410 that the 1E and 2E pins are "enable pins".
Here a link to a better picture of the board.

https://picasaweb.google.com/lh/photo/s72NQLJKjSPpQCyF2eq0b_UuKLp8MgVFzxmX_2DkkFM?feat=directlink

Hope that helps someone figure this out.

Fred

PJAllen · 2011-05-24 05:47

I think that making "D" hi or lo changes the motor direction,
that applying PWM to "E" varies the motor speed,
and "R" is Return/Ground/Signal Ground.

LoopyByteloose · 2011-05-25 06:41

At some point, you are going to have to reverse engineer the schematic for yourself. While there is indeed an H-bridge chip at the core of this, the other logic chips could be used in a variety of ways that only the original designer intended. Just take on the project as a puzzle that has to be unfolded. And it seems you have a few isolated inputs for protection from excessive voltage.

fschutzman · 2011-05-26 10:18

At some point, you are going to have to reverse engineer the schematic for yourself.

The above is obvious but I actually was hoping someone would say,"Oh, I have used that board myself." I think PJ, gave the most useful input. Telling people they should do it themselves is not very useful.

Fred

RobotWorkshop · 2011-05-26 10:48

I can understand that you had hoped to find someone familiar with that board. With the variety of boards out there and the fact this was from some unknown ebay seller your best option is probably to start tracing out a schematic by hand. It certainly doesn't look very complicated and shouldn't be too hard to trace out. You've already found the datasheets for the chips so you have the pinouts. I'd mainly focus on the schematic on the h-bridge chip input side since the output appears to be pretty typical. My guess is that the CMOS chip may be wired to act as a couple of inverters which is pretty common with that chip. If you look at the motor control schematic for the Handyboard here:

http://www.handyboard.com/oldhb/schemv12/motor.gif

You will see the inverters used for each h-bridge chip.

If you don't want to trace out the board then you may want to try and go back through old e-mails or your ebay feedback to get the sellers user name to see if you can contact them through ebay.....

PJAllen · 2011-05-26 11:46

Fred,
I'd like you to get a DCvoltmeter and a 12V power supply.
Place the board on a non-conductive surface.
We're going to find out if those pins are pulled-up or what.
1) Connect 12V to the 12V terminals on the board.
2) Then put the DCvoltmeter on those connector pins:
1D to R = ____V
1E to R = ____V
2D to R = ____V
2E to R = ____V
and report back same or don't.

If you have better things to do, we can stop right now; just say "Enough" and we're done.

LoopyByteloose · 2011-05-27 00:51

Admittedly, it would be wonderful if someone happened to have the same board, but the point of reverse engineering is that it is really the only other way to fully comprehend the board. The photos are nice, but we still can only guess on the routing of circuitry. Labels may be right, or may be in error.

My comment was not meant to throw this back at you in a mean spirited way, but to point out that reverse engineering is of value and often necessary. I've done it with quite a few boards and usually it only seems more difficult than it really is.

identify h-bridge controller inputs

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