Another old project. This is a modified power strip that allows to control each of its six outlets independently via a serial port. The outlets are controlled with TRIACs. There is no heat sinking so it can only handle relatively low power loads. I had no problems using it with 60W lamps, but the original purpose was to automatically turn off my soldering irons (25-50W), which very often I left connected, hot and forgotten for days in some cases.
I've posted the schematics, and firmware source code.
Originally I built this 8051 based circuit during September 2000. This thing has been shelved for a long time. In theory this is a really simple and trivial project but it can be troublesome to package all of its parts inside a common power strip. At the moment I got a cheap power strip that had round and flat prong compatible outlets.
Originally the circuit was directly soldered to a perforated board.
Not that bad, but if you lift the board...
Some of those wires carry 220VAC and some are part of the digital circuit. So I was undestandably concerned about powering it again, after so long a time. So I decided to remove that and make a PCB. Some of the TRIACs were also shorted, so I decided to change them.
Here is how it looked before I reworked it.
I simply copied the old circuit to KiCAD. Next image shows the schematic.
Then I hand routed the PCB.
The finished single sided PCB:
The completed circuit, now much cleaner and safer, not ideally though:
The power strip completed.
Fully assembled and working.
I later realized that I forgot to put two pullup resistors for the pins P1.0 and P1.1 of the ancient AT89C2051 microcontroller. It was necessary to add those later.
As can be seen the circuit is as simple as RS232 interface, microcontroller, buffers and optoisolators. The optoisolator interconnections shown in the schematics are good for BTA134 sensitive gate TRIACs. As I couldn't find those in local stores I ended up using the BTA136 which are non-sensitive gate TRIACs that require a different circuit. In this case the common connection is removed and each TRIAC is connected directly to an optoisolator. I didn't put any snubber, so it is safe to use with resistive loads only. The transformer is from a cheap 250mA AC to DC converter and the output is selected so at the regulator input it measures 8.5VDC.
To turn on an outlet it is necessary to send a 55H followed by the number of the outlet (0 to 5) and to turn off an outlet send a 54H followed by the outlet number. There is no permanent memory in the microcontroller, so whenever it is power cycled or when a reset occurs for any reason, all the outlets are disabled.
; ROLANDO CALLA Z/ LPB / 15-9-2000
;***********SER INT VECTOR***********
WAITTI: JNB TI,WAITTI
;***********SER INT END***********
WAITTI2: JNB TI,WAITTI2
WAITRI: JNB RI, WAITRI
WAITRI2: JNB RI, WAITRI2
Programmed in Turbo Delphi, a very simple standalone application that detects the strip and sends commands.
Circuits that control 110-220VAC devices using TRIACs or other components can be very dangerous, if you are not so experienced with this type of circuits, find some knowledgeable person to help you to do it safely.