Controlling H-Bridge with RS232 signals (without uC)

Discussion in 'The Projects Forum' started by aut0pilot101, Feb 23, 2009.

  1. aut0pilot101

    Thread Starter New Member

    Feb 23, 2009
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    Hi, everyone. I'm controlling H-Bridges with RS232 signals. Until now, I've been using a microcontroller to perform this task, but I think it's possible to bypass the microcontroller entirely. Doing so would be very cool.

    Anyway, I've been looking at the HD-6402 as a possible replacement for the uC. It takes in a byte of serial data, and then sets 8 discrete, parallel, digital signals (RBR1-RBR8, one for each bit). All without software!

    Each of these signals could control a pair of transistors for a total of up to 4 H-Bridges, but I have some questions first:

    1) The 6402's RRC pin needs to be attached to an external clock running at 16x the data rate. Can anyone refer me to such a clock, assuming I'm using 9600 baud? Do they make RS232 interfaces with internal clocks? (I wouldn't mind having a fixed data rate.)

    2) I need to pulse the 6402's master reset (MR) signal, but only once when the device starts up. Is there a good way to do this automatically when I connect my power source? BTW, I could add a pushbutton to get around this problem temporarily. Not really a critical item.

    3) I don't want all of those transmission and control pins floating around. And I don't want to have to tie half of the device to the rails. I would be much happier with just the receiver half of the component. Can anyone point me to such a device?

    That's all for now. Thanks for reading! I look forward to your suggestions, comments, criticism, fan mail, love letters, etc...
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    But, what would that do to your parts count?

    Yep, interesting - but it requires an external clock. You can get uC's that have internal clocks. Right there your parts count gets ramped up, and your reliability heads towards the toilet.

    The 6402 is a UART, and has been around for a long time. uC's are relatively new, and incorporate many capabilities that are not found in such dedicated function ICs.

    Might be done with a simple RC circuit. But, that's another couple of components that you wouldn't need if you were using a uC.

    Not offhand, as that's the nature of UARTs.

    Welcome to the Forums. :) It's a fun place, even if some of us "old coots" come off as a bit ornery. ;)

    Seriously, take a look at some of the newer offerrings from Microchip; you can pick/choose nearly every feature you want, and reduce your parts count to just a single uC and perhaps a voltage regulator & I/O caps.

    I have a large selection of TTL and CMOS ICs that are just sitting in drawers; their functions have been replaced by uC's.
     
  3. aut0pilot101

    Thread Starter New Member

    Feb 23, 2009
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    0
    Thanks for the timely response!

    I already have the circuit working with a uC, but I would like to free it up for use in other projects. Also, my uC takes up quite a bit of space, since it is still attached to a massive prototyping board. And space is the biggest issue, since the entire assembly has to be mounted with a laptop on top of a small RC car.

    What it really boils down to is whether I want to develop a smaller prototyping board or this circuit, since I'm not going to be moving past the breadboard/prototype stage.

    Besides, don't uC's which allow serial communication come with a UART on board anyway?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You just happen to luck out - sometimes it can take days to get a response. ;)

    You must have a Parallax uC - they're expen$ive. (Yes, I have a couple of them too.)

    Nowadays, you can obtain uC's that are extremely compact for the functionality they contain, for very low cost. How about a 44 pin 8-bit uC with 8k ROM that will easily fit on your thumbnail, and that costs a buck or two?

    Space, the final frontier. ;)

    Yes, but they're easier to use - and can perform a lot of other functions besides. Instead of having to worry about tying half of the pins to rails, you can think up something useful for the pins to do - or just leave them floating if you don't need them.
     
  5. aut0pilot101

    Thread Starter New Member

    Feb 23, 2009
    8
    0
    I've found a website which details interfacing RS-232 signals to logic circuits. It's been very helpful. Here's the URL, in case anyone finds a need for it: http://beyondlogic.org/serial/serial1.htm

    Thanks for the warm welcome, Sgt.
     
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