H-Bridge turning heads

[wseay]

Howdy all:

I have a Prop1 that I am turning into a dedicated Prop controller for a Santa.  I can turn the head left & right and there is a 'center' indicator switch to tell me when I'm looking straight.  Santa is a 12 Volt kinda guy.

I have rigged up a mechanical H-Bridge using two relays with N.O/N.C. contacts.  If move these relays to the Prop1, do I need to provide protection diodes?  Or is there a cleaner solid state way to do this?

Thanks...

[JonnyMac]

The the relays you're using draw 250 mA or less you can connect them right to the Prop-1 outputs (green terminal blocks, V+ is common).  The ULN2803 has protection diodes built into it, so you're in good shape.

[wseay]

Thanks Jon!

My daughter wants me to get rid of the clicks.  That's when I remembered I had some of these on hand:
TEXAS INSTRUMENTS  QUAD HALF-H DRIVER/LINEAR #SN754410NE
Spec Sheet: https://www.jameco.com/Jameco/Products/ProdDS/1054684.pdf

I going to mock up a perf board to replace the relays.  Pins 2 & 7 go to the Prop1.  Pins 8 & 16 to V+.  Pins 4, 5, 12, 13 to Gnd.  Then I will make pin 1 high with a resistor to V+.

Now the question.  Do you have a formula that would help me find the appropriate value for my pull up resistor?

Walter...

[JonnyMac]

You should connect Vcc1 (pin 16) to +5 volts, not to V+ (see the spec sheet, the max on Vcc1 is 5.5v).   Pin 1 doesn't need a pull-up unless you intend to connect a push-button between pin 1 and ground (this would be useful to let the motor coast by disabling the outputs).  If you are going that route, a 4.7K or 10K will be fine; it's a level-sensitive input.

[wseay]

Thank you Jon!

I have been a software engineer for decades.  Dabbled in the hardware (BASIC Stamp Discovery Kit and a lot of N&V articles).  So I appreciate your patience in helping me get my wires uncrossed!

I'll try to post pics when I have it working.

Walter...

[wseay]

It works!!!  And the chips aren't getting hot!! (Been down that road)

Right now its on a really messy breadboard.  Need to move it to something cleaner before I take a picture.  I'll see if I can create a schematic as well.

Thanks to Jon and John for creating such a well thought out product line.  I can't believe how easy it was to dive in a get results!

Next is the RS485 network to use these with Vixen.

[livinlowe]

Have you seen Jon's January column in Nuts and Volts? He is starting a series of articles on RS485. Its a good read!

[JonnyMac]

I don't plan on doing a series of articles on RS-485; the communications were covered -- pretty well, I hope -- and there's no need to pound that any harder.  The "long journey" I refer to is my personal development of modules for my home.

[livinlowe]

Oh, my bad.  ;D