CPLD motor control

[Chris] continues cranking out the tutorials, this time around he’s showing how to use a CPLD for simple motor control. The demo hardware is pretty basic, he built his own FPGA/CPLD demo board a few years back which used a PLCC socket for easy interfacing. You should be able to use just about any gear you have on hand.

Of course the thing about these chips is that you’re working with hardware that can be run in parallel. [Chris] mentions that this is what makes it perfect for timing-critical applications. Here he’s using a motor driver that monitors a PWM signal, using the duty cycle to actuate the direction and speed at which the motor turns. After the break you can see a demonstration of the CPLD reading from an ADC chip and converting the value to a PWM signal. [Chris] has also used the same hardware for VGA signals; something that is usually a timing nightmare if done with a microcontroller.

If this leaves you thirsting for more CPLD goodness check out our own guide on the subject.

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Motor controller also does nyan cat

As a freshman at UC Berkeley, [Keegan] has been helping out with his school’s Pioneers in Engineering program that gives high school students some hands on experience with engineering principles, usually by building robots. This year, [Keegan]‘s project is a motor controller that just so happens to play the nyan cat song over the motor PWM output.

The motor controller is meant to replace the Pololu simple motor controller the PiE team is currently using. Onboard is an H-bridge chip and an ATmega328 that takes commands from an I2C bus. The ‘328 is loaded up with the Arduino bootloader making the firmware very accessible – a good thing for the high school students that will be building and programming these robots.

[Keegan] put up the Eagle files for the board up on the PiE Wiki. For now, just enjoy the dulcet tones of the pop tart cat theme song after the break.

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Repair a misbehaving motor controller board

It can be a real drag to fix a circuit board which has stopped working as intended, especially if you don’t have any reference material for the product. That’s the position that [Todd Harrison] found himself in when the controller for his mini-lathe gave up the ghost. He undertook and hefty repair process and eventually mapped out and repaired the driver board.

First off, we’re happy to report his success at the end of a year-long troubleshooting process; the entirety of which occupies six different posts. The link at the top is the conclusion, and you’ll find his final test video after the break. But as you can see from the image above, he was met with a lot of problems along the way. The first two segments show him reverse engineering the PCB, with a giant schematic coming out of the process. In part 3 he then started probing the board while it was live, with the smell of hot electronics causing him to disconnect the power every thirty seconds. One time he took too long and blew a resistor with the pictured results.

In the end it was a shorted PWM chip to blame. He tested a couple of different replacement options, dropped in the new part, and is now back in business. [Read more...]

Motor drivers: half h-bridge with brake and more

Here’s a nice little circuit that will drive a motor and allow you to stop its rotation, giving your robot a set of brakes. It’s part of [JM's] post about the in’s and out’s of building microcontroller friendly motor controllers (translated).

This particular setup is a half H-bridge. It allows you to drive the motor in one direction only. The MOSFET used on the ground-side of the motor doesn’t actually need to be there. This is the brake which let you electronically stop the motor from spinning. Without it, the motor will keep turning under its own momentum when the half-bridge is shut off. Depending on the application this can be a big problem. There’s a great demonstration of the circuit braking a fast spinning motor in the video clip below the fold.

It is possible to use this driver with PWM, but [JM] has some warnings about inbuilt functions like FastPWM. Make sure you read his admonition, and if you need a refresher don’t miss this Hackaday video segment.

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Tinywrench controls motors with ATtiny24 chips

Tinywrench is [Tanjent's] take on a motor controller board. It aims to replicate all of the functions that a standalone motor controller chip offers at as low a cost as possible. Early results are in. It works, and as seen can be assembled for about $8.

The top of the device offers a terminal block for connecting motors, ground, and 24V input. A pin header on the bottom has all the connections you would expect to find with a stepper motor driver board. Looking back on top there’s also a pair of ATtiny24 chips, each with its own trimpot for balancing the constant current output. Hiding on the underside of the board are two H-bridges built using high and low-side MOSFETs along with some diodes for protection, and various passive components for driving them.

As it stands, each of those H-bridges can handle around 9 amps which should be more than enough for projects with small motors. [Tanjent] mentions that one of the main advantages of working with this instead of a single motor-driver chip is that if you fry one of the MOSFETs you can replace it instead of trashing the entire board.

Intro to DC motor control using the SN754410

So your electronic hobby skills are coming along quite nicely but you’re not very comfortable doing more than blinking a few LEDs. Now’s a good time to try something new by driving a couple of DC motors.

You probably know that you can’t just hook these up to the pins of your favorite uC and call it good. The motors draw a lot of current (especially if they’re strained in lifting a heavy load) which would burn out your logic circuitry. Add to this the excess induced current that is generated when a spinning motor is shut off and you’re going to need a control system that can handle these dangers.

Enter the h-bridge motor driver. [Chris] has guided us through the process of building and using a H-bridge in the past. This time he’s using a motor controller that has four half H-bridges built into it. He hooks up the SN754410 to two motors, giving him speed and direction control for both based on the duty cycle of a PWM signal entering the chip for less than $2.50. Check out the video after the break for an overview of his methodology, then work your way through the multi-page post that he recently published.

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Reversible relay-based motor controller

[Nothinglabs] built this motor controller as an alternative to using an H-bridge. They call it the RAT controller which stands for “Relay and Transistors”. You can see above that two Darlington transistors along with their base transistors allow logic signals to switch the relay on and off, driving the motor in one direction or the other based on the open or closed state of the relay. See it working in the video after the break.

It’s a nice little workaround with few parts, but because the relay is mechanical there will be a short lifespan when compared to solid-state motor controllers. That’s okay, because the motivation here was lack of parts on hand, rather than an increase in performance. It’s also worth mentioning that all of these parts can be purchased at your local Radio Shack when you don’t want to wait for component orders by mail. We certainly appreciate that it takes far few components than [David Cook's] H-bridges. His designs are our favorite – we’ve used them in our own projects – but for quick and dirty you can’t beat five components and the short assembly time needed when using this type of dead-bug style soldering.

[Read more...]

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