Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

The digital temperature controller looks nice and hard to figure out, but I'm going to use my multimeter's thermocouple (the first time I've ever used it) to watch the temp, and use a mechanical switch to bypass the thermal limit, in addition to the 150C new bimetal switch that is in the mail. I saw an easy to use (hardly adjustable) analog temperature controller on ebay for $15 that accepts an L thermocouple which is outdated but within a couple degrees of type J.

== Motor Speed ==
I used a 555 timer in astable mode with a bypass diode (see wikipedia) to get <50% on time, to control a relay to turn the motor on and off to more slowly feed the PCBs. After reading a little about synchronous motor speed changing, this seemed by far simplist method. This model's 12"/min means 5 mm per second, which means the width of a PCB hole is covered in less than 200 ms. After experimenting, I found the shortest possible on time for this motor and gear assembly without skipping is 150 ms, which is 9 times longer than 1 AC cycle of 17 ms which the motor can't even theoretically get down to. So, I can make it feed 1 hole width and stop for however long I think the rubber next to the heating elements is not melting. Others have said 4 or 5 passes is needed, so 4 times off-to-on ratio seems about right. Maybe less since multiple pass allow cooling. I'm drilling a hole in the laminator's plastic case to include a potentiometer adjustment to control the 555 circuit to go from the motor being constantly on (POT at zero, the "off" time) to about 4 times longer than the "on" time. This has worked out a lot better than I expected, but I haven't tried it to see how bad it might create lines from stopping and starting. It might depend mostly on the transfer method and chosen temperature.

My parts list, which I had on hand:
LMC 555NC to burn out before realizing my 12V adapter puts out 16.3V under low current conditions.

LM555 which can take 18V instead of 15V
12VDC relay capable of driving 6A 120VAC
1 uF for astable
220k for on time (150 ms)
1M pot off time (693 ms)
diode