Bonded Heat bed for 12"

[printbus]

PWM (Pulse Width Modulation) will vary the ratio of on time to off time in a pulse train, not the frequency of the pulses.

Regarding Solid State Relays, note that for use with the existing 12V DC heater, you'd have to be sure to buy one meant for controlling DC outputs, not AC. A DC SSR will likely use a MOSFET. An AC SSR will likely use a triac. SSRs are really nothing but the MOSFET or triac with driver circuitry in a standalone package. As an example of one, here's the one often recommended for use with the PWM heater output on Smoothieboard - http://shop.uberclock.com/products/solid-state-relay-dc-to-dc.

[lakester]

Do the common arduino boards (aka RAMPS, RUMBA, etc) provide circuitry that facilitate the generation of a PWM signal?

Probably breaks down to two questions:

1. Is there a performance hit on the cpu to generate a PWM signal for the heat pad (apart from some minor math computing the heating values)?
2. In addition to the SSR, do you have to relocate the HB "signal" wiring to a different spot on the controller board that does support PWM, if the current location does not?

Have been googling a bit, and I can't tell for sure if there is any "helper" hardware on the common boards..., or whether the PWM is entirely software implemented...

[lakester]

Hmm..., think I have the answer.

Looks like it is a soft pwm...., a quick scan of the code doesn't reveal anything driving specialized pwm hardware. Freq is around 7hz..., I guess that, masked in with the other soft pwms (e.g., for the HE), that amounts to writing to a couple of ports a few times a second, without especially critical timing requirements. So, I'm guess'n it doesn't hurt performance much.

Cool.

I still think a PLA on blue tape test is worth doing, to see if it's worth going to any trouble in this regard at all.