If you haven't looked at it, try the Wikipedia (do a websearch for "wiki h-bridge") for a discussion of h-bridges.
There are links to various circuits and further discussion. I believe there's a Nuts and Volts Column on h-bridges.
Go to the main Parallax webpage, choose the Resources tab and look in the list for Nuts and Volts Columns.
You'll have to browse through the different titles, but there's a tremendous amount of useful information there.
I'll tell you what. For a good fundamental (and cheap way) understanding of how an h-bridge works I'd get a good size breadboard and 4 npn transistors & 2 pnp transistors, some diodes and resistors and go at it. This is basically out of the book "123 robotics experiments for the evil genius". I'm a mark tilden fan anyway and i think first if u get a good grasp of basic analog electronics ...then u can always scale up. This is how i did MY first one atleast. Good luck!
Dave
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ "THE ONLY TRUE WISDOM IS IN KNOWING YOU KNOW NOTHING." - SOCRATES
If you're in a time crunch, I would just use the SN754410. It can only handle an output current of 1A so if you need to go higher, you'll have to look in other alternatives. Otherwise, it's quick and simple.
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"It's not procrastination, it's a tactical delay." ~Worf
That's a temptingly simple circuit, but the copy says it's limited to 150 mA (barely a trickle of current), while the supply voltage is high (9-18 volts).· Unless you have a tiny robot with special high voltage, low current motors, I'd steer clear.
At the risk of repeating myself here in the forum, I'm a huge·fan of using SPDT relays for H-bridges. The circuit I'm attaching works great using Radio Shack parts (easy to find) and provides for dynamic braking of the motor. The only compromise is no speed control. Full on, full off. If I need one lower speed, I'll throw in an extra speed relay with a few diodes to drop the voltage.
Anyhow, this is an easy circuit to make, very robust (relay contacts are your only limiter) and there's zero voltage drop so you get full battery power. Most motor controllers (including the 293 and 754410) can't make that claim.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·"If you build it, they will come."
I'd also recommend Mr. Cook's excellent "Intermediate Robot Building" book. There are several chapters on building and testing H-bridges, from bipolar to MOSFET to IC designs. The various tests and comparisons of the different types are really interesting. It's a great reference for anyone who is getting started with motor drivers.
Erco's design is pretty clever as well. I may have to run to Radio Shack this weekend for some parts and try it out myself!
Mike: It's more straightforward than clever, but thanks for your interest. If you like the concept and don't mind some legwork, it gets even better. Instead of Radio Shack relays, locate some AROMAT or NAIS 5-volt DIP relays (TF2-5V, ATF209), which have extra-sensitive polarized coils. The coil resistance is 320 ohms, and each relay only draws 16 mA, so you can drive them directly with the Stamp i/o pins. No driver transistors or 330 ohm bias resistors are required.
I buy them in lots off eBay, as little as 25 cents a relay. Watch those part numbers, though. Aromat/NAIS make lots of different relays, some of them are latching types.
If you have a big batch of them, you can hand-pick the most sensitive ones (~5%), and these can even be reliably driven directly by the BS1 Project board or the BS2 Homework board, which have series 220 ohm resistors on each pin. Those are ultra sensitive relays!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·"If you build it, they will come."
I use SPDT relays for simple on-off, forward-backward motor movement. For loads under 5 amps, I use the Infineon TLE-5206-2. It's got a very small footprint and some good features.
For high loads, up to 25 amps, I use the Parallax HB-25. Great design, one wire control, you can run two motors off of just one pin from the MCU, built in heat sink and cooling fan, uses same control as a servo, and just one line of code will get your motor running.
Wow, those sound like pretty interesting relays. They must be discontinued, I can't find them stocked at any of the usual vendors. Too bad, but I'll keep my eyes open for some surplus!
They are expensive if you can ever find them from Mouser or Digikey, like $6 or more each. Some people on eBay are still charging fantastic prices. I first found them at Hosfelt years ago (no more there now) and they pop up in lots on eBay periodically. They have DPDT contacts, BTW. Here's a similar-looking one·from eBay:
These numbers are different, so I can't say how these work,·but at least now you know what they look like. They plug into a standard DIP socket, which is handy.
There's·a different relay at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280235577448·.· These appear to work similarly, but they are narrower than the ones previously mentioned and won't plug into a standard DIP socket. They are 0.200'' wide, not 0.300".
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·"If you build it, they will come."
Comments
There are links to various circuits and further discussion. I believe there's a Nuts and Volts Column on h-bridges.
Go to the main Parallax webpage, choose the Resources tab and look in the list for Nuts and Volts Columns.
You'll have to browse through the different titles, but there's a tremendous amount of useful information there.
Dave
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"THE ONLY TRUE WISDOM IS IN KNOWING YOU KNOW NOTHING." - SOCRATES
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"It's not procrastination, it's a tactical delay." ~Worf
At the risk of repeating myself here in the forum, I'm a huge·fan of using SPDT relays for H-bridges. The circuit I'm attaching works great using Radio Shack parts (easy to find) and provides for dynamic braking of the motor. The only compromise is no speed control. Full on, full off. If I need one lower speed, I'll throw in an extra speed relay with a few diodes to drop the voltage.
Anyhow, this is an easy circuit to make, very robust (relay contacts are your only limiter) and there's zero voltage drop so you get full battery power. Most motor controllers (including the 293 and 754410) can't make that claim.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·"If you build it, they will come."
www.robotroom.com/BipolarHBridge.html
I'd also recommend Mr. Cook's excellent "Intermediate Robot Building" book. There are several chapters on building and testing H-bridges, from bipolar to MOSFET to IC designs. The various tests and comparisons of the different types are really interesting. It's a great reference for anyone who is getting started with motor drivers.
Erco's design is pretty clever as well. I may have to run to Radio Shack this weekend for some parts and try it out myself!
Mike
I buy them in lots off eBay, as little as 25 cents a relay. Watch those part numbers, though. Aromat/NAIS make lots of different relays, some of them are latching types.
If you have a big batch of them, you can hand-pick the most sensitive ones (~5%), and these can even be reliably driven directly by the BS1 Project board or the BS2 Homework board, which have series 220 ohm resistors on each pin. Those are ultra sensitive relays!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·"If you build it, they will come."
For high loads, up to 25 amps, I use the Parallax HB-25. Great design, one wire control, you can run two motors off of just one pin from the MCU, built in heat sink and cooling fan, uses same control as a servo, and just one line of code will get your motor running.
Daryl
Wow, those sound like pretty interesting relays. They must be discontinued, I can't find them stocked at any of the usual vendors. Too bad, but I'll keep my eyes open for some surplus!
Mike
http://cgi.ebay.com/15-pcs-AROMAT-TF2E-4-5V-1-H50-4-5-VOLT-8-PIN-RELAY_W0QQitemZ110265475078QQihZ001QQcategoryZ36328QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
These numbers are different, so I can't say how these work,·but at least now you know what they look like. They plug into a standard DIP socket, which is handy.
There's·a different relay at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280235577448·.· These appear to work similarly, but they are narrower than the ones previously mentioned and won't plug into a standard DIP socket. They are 0.200'' wide, not 0.300".
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·"If you build it, they will come."