As some of you will know, I write (and sell) PIC tutorials: www.gooligum.com.au/tutorials.html. =20 I've just started working on a PWM lesson, using the 16F684, and am thinkin= g about what examples to include - and I'd really appreciate any thoughts/feedback! =20 Simple single-output PWM is easy enough. To show the effect of changing duty cycle, dimming an LED works well. And to show the effect of changing period, using the PWM output to drive a piezo speaker is effective - I've written a little example that changes the frequency as a pot is adjusted. =20 Simple (no dead band) half-bridge output is also easy to demonstrate - driving a piezo push-pull fashion makes it obviously louder. =20 However - people want to know how to drive motors. I've had requests for tutorials about driving RC servos, but I think I'd do that as a separate topic. Just good old-fashioned brushed DC should do to start with. =20 Motors aren't quite as simple to drive as an LED though, and this is where I'm wondering what the best approach is. =20 For single-output, I could specify a MOSFET and flyback diode, or a motor driver such as an L293D. Any thoughts? =20 For half-bridge motor control, I'm thinking that the L293 is the way to go. The two complementary PWM outputs on the PIC connect to two inputs on the L293, with the motor between the L293's outputs. It would go full speed forward with 100% duty cycle, stop at 50%, and full reverse at 0%. That's the theory, anyway. I've never used a half-bridge PWM for motor control before. That arrangement seems quite inefficient, because it's pushing current through the motor 100% of the time (50% one way, then 50% reversed)= , even when its stationary. That also seems to be true of the "half-bridge output driving a full-bridge circuit" shown in the 16F684 data sheet. Am I right? But does it work well enough anyway? Also I'm not sure, if I go with the L293 arrangement, whether dead-band delay is relevant. It certainly would be best to mention it in any tutorial, and I understand about shoot-through current and can explain why that's to be avoided, but if I'm not using MOSFETs to build a half-bridge, is there any practical way to explain the potential need for dead-band delay, that relates back to the L293 circuit? =20 As for full-bridge, I'm leaning toward using discrete MOSFETs, although it would end up being a little cumbersome if breadboarded. I'm assuming P-channel on the high side and N-channel on the low, to avoid the need for drivers - that for a low-power (small hobby DC motor) app, the 20 mA that the PIC pins can supply is adequate to switch logic-level MOSFETs quickly enough. I'm also wondering whether, in a low-power application like that, the MOSFET's body diodes will be able to handle the flyback current, or if external diodes are necessary. My aim, since this is a tutorial on using PWM, is to keep the electronics as simple as possible, but no simpler. By the way, I'm assuming a single 5V supply for PIC and motor, but obviously with some decoupling around the motor. Again, not designing for field reliability, just a simple lash-up, but I don't want the PIC resetting ever= y few seconds due to power supply noise, either. =20 Does any of this make sense? Anyone have any better suggestions on demonstrating PWM in a simple way, that doesn't use a lot of hardware that students may not have (or buy cheaply)? =20 =20 Thanks in advance, =20 David Meiklejohn www.gooligum.com.au =20 =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .