Shop Learn
H-Bridges of Madison County: 77 Cents — Parallax Forums

H-Bridges of Madison County: 77 Cents

ercoerco Posts: 20,013
edited 2018-04-29 23:29 in Robotics

I'll be forced to unfriend anyone who doesn't order at least ten units.

Oh sorry, wrong social media.

I'll just keep on Tweeting until everyone confirms buying ten.

Oops. My bad. Snapchatters, snap off a few of these...

What? Wrong forum again? DOH!

I've been impressed using these MX1508s in some prototypes lately. I've stalled toy grade motors on 5V and they don't mind at all. Heck, you can barely buy a single decent MOSFET for 77 cents. These can coast or brake, BTW.

Fake Chinese specs, use at your own risk, but I wouldn't push it:

Supply voltage 2V ~ 10V, can drive two DC motors or a 4-wire 2-phase stepper motors ,can achieve forward rotation or reverse rotation, it is possible to adjust the rotation speed. Each can provide continuous current of 1.5A, peak current up to 2.5A



  • ercoerco Posts: 20,013
    edited 2018-04-30 15:13
    It's a wee bit funny that the Ebay listing title doesn't even use the term H-bridge. This seller and other websites incorrectly call this obscure little part an L298N or L293. :)

    From :

    Products introduction: motor drive module very for in battery power of intelligent car, and toy car, and robot, above using, power voltage 2V~10V, can while drive two a DC motor or one 4 line 2 phase type step into motor, can achieved pros and cons turned and adjustable speed of function, each road current can to 1.5A continued current, peak current can up 2.5A, has hot protection and can automatically recovery.

    Between to and fro PLUS pros and cons, this baby does it all!
  • Didn't I already buy these? They look like the ones you posted about a month or so back.

    I will admit not to buying 10. For my use 10 would be hording, and hording is a bad habit. My old 5 bedroom, 2 1/2 car garage house was a testament to that.
  • ercoerco Posts: 20,013
    Pardon ,yes they are the same, but my previous post was lost in another wacky convoluted erco thread about dummy batteries. I couldn't even find it to look up the truth table, so when I found them recently for much less, I figured surely they deserve their own thread. Especially because there are several new forum threads asking questions about driving motors, etc.
  • Oh, I don't mind the dupe, it's just that I distinctly remembered already ordering these!

    I got four, which is several more than I'm likely to use. Sadly, I can't write about them in published work because likely they'll be gone or altered for any kind of decent shelf-life for a book or even article -- 'tis the nature of eBay. Gotta relegate them to my personal stash. That said, it's nice to get an H-Trestle for a buck.
  • ercoerco Posts: 20,013
    That said, it's nice to get an H-Trestle for a buck.

    A Canadian buck, that is! Worth smoke testing at that price. This Russian fellow appears to like them too. At the end of his video, he "hot wires" the H-bridge with a single wire to B+, demonstrating that the input pins have integral pulldown resistors.

  • GordonMcComb wrote: »
    That said, it's nice to get an H-Trestle for a buck.
  • K2K2 Posts: 684
    erco wrote: »
    It's a wee bit funny that the Ebay listing title doesn't even use the term H-bridge. This seller and other websites incorrectly call this obscure little part an L298N or L293.
    Terribly unfortunate. I would have passed right over this listing. Thanks for bringing it to the attention of the forum.
    Between to and fro PLUS pros and cons, this baby does it all!
    Best laugh today. Wife thought it was funny too. (She lived in China for a few years. She and a girlfriend would laugh themselves silly reading Get Well Soon cards translated into English.)

  • K2,

    It cracks me up sometimes the way they translate things such as datasheets.

    On the other hand, apparently DMV translations were done using Google.
  • ercoerco Posts: 20,013
    For classic translations, see also and watch out for those Skid demons, hi hi hi!
  • GenetixGenetix Posts: 1,547
    edited 2018-05-06 06:59

    You've posted that before, it's funny.

    Did you ever see the EEVBlog episode where Dave was mailed a Cen-Tech multimeter?
    He makes fun of the safety rules.
    "Don't work alone...................I'm screwed!"
    "You have to wear the proper safety equipment when using a multimeter."
  • ercoerco Posts: 20,013
    Just for sport, hoard a few full-sized L298Ns for $1.74: The heat sink alone is worth it!

    from specs at


    800 x 800 - 36K
  • I bought some of those L298 modules awhile back. They are pretty bulky. And now, thanks to the blurb about the other module, I'm also worried about "high fever." Maybe I'll order some of those, too, to compare.

  • K2K2 Posts: 684

    Yup. You definitely don't want "very burn" in your high-reli application.
  • Good to know I can replace the entire motor controller for less than I paid for the 3 position terminal block I ordered to fix it...

  • ercoerco Posts: 20,013
    Just took in a quickie freelance "project on a budget" which will use one of the many L298Ns I have on hand. Of course I re-hoardered 3 to take its place.

    Expect to see it at Maker Faire San Mateo this month!
  • Cool! Let us know where it will be. I'm exhibiting too.
  • ercoerco Posts: 20,013
  • ercoerco Posts: 20,013
    edited 2018-05-08 17:39
    "A pin saved is a pin earned." Benjamin Franklin

    Adding two diodes per H-bridge on the L298N lets you select coast or brake without using a third micro connection to the ENable pin. Truth table attached. The stock L298 module comes with two removable jumpers which connect both ENable pins to +5V, which turns dynamic braking on all the time. Even during the OFF periods of PWM. That's pure madness, causing unnecessary mechanical wear & tear on the gearmotor.

    BTW, according to , the L298N's built-in 5V regulator is only good for input voltages up to 16V. Glad I caught that and removed the default jumper before connecting to 28V for the smoke test.

    1200 x 420 - 48K
  • tonyp12tonyp12 Posts: 1,950
    edited 2018-05-08 19:45
    Lowest price for a comparable part on Mouser is 84cents/each for 100units:

    Runner-up at 87cents but with current sense and internal pwm.:

    MX1508 can be had for 21cent/each for 100units shipped free from China:
  • It's a nice fix with the enable lines and they should ideally bring those out. The L298 was meant to apply PWM to the enable lines.

    I'm thinking you always need to PWM the line that's HIGH, which means your MCU has to have four pins with PWM instead of just two (if you want speed control for reverse and turns). On some controllers that's not a problem, but on an Arduino there are only some pins with PWM, and they're connected to specific internal hardware timers. You'd use two (of the three in an Uno) just for this.

    Such is not a problem in Propland, and I think any PICAXE M2 part will have no trouble.
  • ercoerco Posts: 20,013
    Yes, two PWM pins per channel for full speed control, meaning four PWM pins to control two motors.

    You miss nothing, Master Roboto!

    I'm not normally a fan of L298s since they drop several volts. That's quite noticeable in a 6V system. But when using these 24VDC system, what's a few volts between friends? They're rated to ~35V, and at the low currents these gearmotors draw, that heatsink shouldn't heat up much.

  • ercoerco Posts: 20,013
    It's a nice fix with the enable lines and they should ideally bring those out. The L298 was meant to apply PWM to the enable lines.

    Ah, so... I see what you mean. If you have more dollars than sense regular lines than PWM lines, then apply PWM only to the enable pin, and set the direction on the IN pins using non-PWM pins.

    Barely related: besides PWM, my current project uses two eBay relay modules. Control signal is active LOW, who knew? I'm really glad they silkscreened screw images by the holes so I know what's supposed to go through there. I just couldn't figure that out.

    2560 x 1920 - 665K
  • Its active LOW for the normally-open connection? Or is this relay just single-throw? I couldn't tell by der piktuur.

    So I'm going to be doing some eBay buying this weekend. I'm going to pick up a few more of these Madison County bridges, plus try to find the Wowwee/Dagu motors with the thinner wheels--the kind Feetech uses on their little circular bot. Have you seen those sold separately on eBay? I found some Feetech converted servos (DC interface) and matching wheels on Amazon, but not yet on eBay.

    I'm also looking for a good source for a buck boost regulator, similar to the bucking stepdown you had noted earlier (and which I got already).

    Finally, any good handle on some cheapo standard (size and non-CR) servos -- the 995s might be good, but I hear the really cheap imports have lousy deadband and aren't at all accurate. I need about 10 to basically ruin, and I ain't doin' that with my Parallax Futaba servos.
  • Some of those relay boards are set up backwards from what you would expect. My template has a way to easily flip the values if a board works that way.
  • ercoerco Posts: 20,013
    These are SDPT relays, triggered by a LOW TTL signal at the control pin:

    Not sure if I left any H-bridges for you to buy... my ten-pack arrived today! I'll actually use most of these on a new project.


    Will look into those wheels. I bought some long ago, can't recall where.

    I've stopped using those 995 servos, they overheat & burn up. I gut them and use them as gearmotors, without electronics. They have gotten worse since they were called the world's worst servo.
    1536 x 1152 - 521K
  • Maybe the active LOW choice was for compatibility with outputs that can sink more current than they can source. Most microcontroller pins are fairly symmetrical these days with 40+ mA drives, so I'm not sure it's all that important for a relay that's activated through a transistor.

    Gotta be better than a certain "Arduino compatible" buzzer I had to use for a project I wrote about. The thing was active LOW, and it it started buzzing before the Arduino could go through its startup routines. Since it was meant to directly plug into the Arduino (no room for a pull-up resistor), it was extraordinarily annoying.
  • ercoerco Posts: 20,013
    edited 2018-05-15 17:22
    Here's a peek at the L298 project I finished tonight for a client. These are the guts for an RC platform that will be at Maker Faire in San Mateo next weekend. This project took longer than I expected for a couple reasons. First, making it bulletproof and obvious for the next guy to install onsite took a while (the chassis and wheels are coming from somebody else). Second, the motor response was hopelessly non linear. Check these PWM values: 1008=100% speed, 180=75% speed, 105=50% speed, 74=25% speed. Mapping those to the RC controller inputs to get decent driveability required lots of testing.

    First video on my new dedicated tech channel, Nytrobotics!

  • I recently picked up some relay modules that support both high and low signal triggering (CTH and CTL), the screw terminals on the right have the same connections as the solder connections). Nice to have that flexibility.

    2037 x 1229 - 585K
  • ercoerco Posts: 20,013
    Speaking of conspicuous bargains, nab a few of these great-looking speakers today! Only 7 left! :)

    Do they really not know?

    1100 x 1100 - 127K
Sign In or Register to comment.