Homebrew PCBs

"demolitron" <ahardinger@...> writes:
> Personally, I love this project as I seem to want to MCU everything I see!

Well, it will show up on my web site eventually.

> With an MCU you could implement a Proportional Integral Derivative
> (PID) algorithm and apply a PWM signal to the Triac giving very fine
> and nearly linear (depending upon the PWM frequency) power control to
> the heater element.

Would I need a 60hz sync signal for this?  Or can it run much slower
than that?

> Using the SPI thermocouple interface would eliminate the need for an
> MCU with an ADC

Need that for the potentiometer reading anyway, and most mcu's come
with adcs - at least, small ones that are "good enough" for a pot
reading.

> as well as the commensurate fussy analog signal conditioning.

Agreed :-)

> If you wanted to save even more cost you could replace the LCD with
> three 7-segment LED displays and replace the POT with two switches,
> one up one down.

The LCD is only $8.30 and I have pots in my junk boxes.  Using an LCD
means I can choose an MCU with fewer pins (less $$) and need a smaller
power supply.

> I don't know what your MCU background is so please forgive me.

I work for Red Hat writing embedded compilers.

> The math for a good PID control is a bit complex for a little 8-bit
> MCU but well within reach.

I tend to use the Renesas R8C chips, which are 16 bit.  I have a spare
R8C/27 from a past project, which has plenty of ram and flash.  20 MHz
clock, 10 bit adc, etc.  32 pins.  Not the cheapest of their chips -
$5.20 - but I already had it, and I've used them for lots of projects
so I have all the tools I need.  It also runs at 3.3v or 5v which
comes in handy.