(Topic ID: 278401)

Big Bang Bar Pal chip???


By Astill

3 months ago



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  • 14 posts
  • 6 Pinsiders participating
  • Latest reply 3 months ago by megadeth2600
  • Topic is favorited by 1 Pinsider

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#10 3 months ago

I think the board, overall is doing the same thing as the circuit described at this link :

https://www.engineersgarage.com/8051-microcontroller/driving-dc-motor-bi-directionaly/

I'm pretty sure BBB uses plain-jane, regular DC motors.

I suspect the PLA is making sure that nothing blows up if both forward and reverse are asserted at the same time.

This is just an educated guess of course. I don't think it is a 2:4 decoder since that's a pretty common, off the shelf part.

#12 3 months ago

"It looks like this could have been done with two ICs"

Agreed .

It definitely looks like the motor driver is an H-Bridge.

I'll be the PAL handles the whole "both FWD and REV" are enabled case (keep the motor off) + simply drives two output pins to enable the forward or reverse side of the H-Bridge. It looks like one of the two outputs has a cap hanging off it to give it a little bit of delay with respect to its partner.

I'm pretty sure you could drive the output of the LM339 to the appropriate inputs of an ST L293D and get the exact same functionality of everything on the PCB in two components and without the PLA (plus some passives of course) .

The ST-Microelectronics L293D is a chip with those 4 big driver transistors integrated into the chip. It also has diodes for that EMP kick that occurs when the motor shuts off. I don't know what the current requirements of the motor are though ... this chip can certainly handle the voltage, but I don't know if it can supply the current . If it can handle it, I'd still heatsink it.

#14 3 months ago
Quoted from TomDK:

I am sure that he also is reading here and, unlike me, he understands what you write !

I hope some of the info I posted helps ... I owe you after the BBB failures on my part .

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