When I was young my dad used a low-tech version, although it was more of a general safety thing rather than to keep me out of it. Basically, he wired the main outlets in the workshop through a switch mounted in a lockable box about 6' off the ground (although I dont' think the box was ever actually locked). It box also had a red indicator bulb to remind him to shut off off workshop power when he was done. This kept some of his older tools from being a potential hazard (fire or otherwise) when nobody was around. Later, he upgraded the circuit to include a GFI when those things became common.
Wow! Thank you William, for using my SCR voltage regulator! I invented it back in 1978. I tried to publish it in EDN magazine back then and they didn't want it. It's loosely regulated, but it is very energy efficient. When the relay is off, you're not burning up power in a zener diode. You already know that you can add a small voltage regulator if you need more precise regulation, like for the microcontroller. You may have seen it used in three of my GF projects, GF#195, the master/slave switch, GF#198, the remote fan control and GF #218, the space heater thermostat. I have used it in a number of unpublished other gadgets that I have around the house as well. Maybe it was a good idea, after all, huh? I've had a couple of people ask me about it. At least one person appreciates it. It's also more robust against power surges than a zener diode regulator. The master/slave power switch and several other gadgets I have that use the SCR circuit have survived many thunderstorms here in Florida, including one that took out half the electronics in my house.
Yours is a great project! Some comments on your ASM code would have been nice, though.
Very cool and practical project. It's quite interesting to see ASM code being used eventhough C is language is common in todays embedded products. Now I have a real world example of ASM code to show my microprocessor class at ITT Tech.
I liked your design used in Gadget #195, much better than the one I have always used to derive appliction poiwer directly from teh line VAC. It provides a lot more flexibility in both available voltage and current. As for the code comments... comments can always be improved. I usually only comment on the major loop or function boundaries and when ever there is a user modifiable variable, table or other issue.
Thanks, William. I recently bought and reverse-engineered a smart outlet strip (i.e. master/slave power switch) to see how someone else solved the problems I had to solve. It used a more complex method to save standby power consumption. It used an opto-coupler and 4 diodes to switch in an extra high voltage capacitor when the relay is on to prevent burning up surplus power in the zener diode when the relay is off. BTW, the high voltage coupling capacitor provides about 20mA per microfarad of available current at 12V0VAC, 60Hz.
I have used assembly in all my appliciations. I have always used MicroChip controllers which have a relatively small instruction set. The applications are ususally smaller, under 200 or 300 instructions and in at least some cases have to be branch equalilized to accomodate timing issues, which harder to control if you program in BASIC or C. MiroChips instruction set has been pretty good to me and is realtively easy to tabulate the instruction execution time. There are also other examples is several other applications both in Gadget Freak#194,137,118,124,159,112,83,88,157,188,200 and another resources, in in Gadget Freaks sister publications, EDN and Test and Measurement. Some of these include a Visual Basic interface which would sit on your desktop.
I agree with you William. I have always used ASM code and I only know how to program PICs. While working for a former employer, I designed an automatic paper towel dispenser according to my boss' requirements. It had all the bells and whistles, was programmed in ASM and used a little more than half of the available 2K of memory. My employer bought a competitor, who was also developing a paper towel dispenser, which I had to debug. It had extremely simple functionality and was written in C. It used almost the entire 2K of memory. Sadly, they closed down the place where I worked and went with the simpler, cheaper dispenser.
Many years ago I build a power lock, but with a different, and simpler, approach. The power switching component was activated from the output of a window comparator. The comparator was fed from a voltage divider, and one of the resistors for the dividing chain was in a 3.5mm audio jack which had to be inserted in a socket for the correct voltage to be set and the power turned on. Nothing more than a transformer/bridge/cap supply, dual op-amp, and relay. basically.
Having kids around the shop can be stressful at best.
I had solved this power problem years ago with store bought devices.
It was more expensive but did not require a lot of mods to the wiring(eg: dual gang box not needed).
I used the X-10 system for the outlets and lighting and just popped off the control keypad from the control switch as I left the shop. I'm a little hesitant to install non-UL/CSA approved parts to my wirng for insurance reasons. Nice job on the solution but can't bring myself to put my house at risk. I learned the hard way, once burned...
I agree entirely with keeping kids safe by securing inherently dangerous items around the house and garage. I've done the same the entire time of having kids in the house, starting with "baby proofing" the house when my children were first born. I've always been sort of a safety fan or buff since being in the Boy Scouts. Safety is something done before an accident...hence the saying "safety is no accident"!
Although it seems like a cool solution to make a home-made switch system for the power outlets in the garage or workshop, I'm not so sure it would meet "code" requirements. If the device is not UL tested and listed, it's probably not legal to use connected to the house power. I think commercially available power locking devices would be better. I have six quad outlets in my garage, so I never have to look for a vacant electrical outlet.
My safety system was to lock-up ALL tools, especially all power tools. I always considered my electric chainsaw to be extremely dangerous, as well as circular saw, saber saw, power drill, etc. Of course, all guns are secured even better than the power tools and hand tools. Also, we always secured our car keys to prevent kids from getting any silly ideas (I've heard many stories of 12 year olds taking the parents car for a drive). As a result, my three daughters (all young adults now), all grew-up in a relatively safe and secure house with no serious injuries...and no kid's friends hurt either.
William, what would be the total cost factor and any precautions to avoid electric shock and to prevent current leakages. If by chance forget the secret code, any resetting mechanisms either for regenerate a new one or recover the secret code.
I think the design is pretty solid. While not an expert I think it is needing a surge/lightning protector, confirmed/qualified materials/parts and $ before it could be considered for certifcation and only if hter was a real market. The relay provides the isolation, leaving the buttons, as the user interface. The 10 ohm carbon resistor, the inductor both add a bit of fusing. The regulator has thermal protection.
As for the code recovery and programming...The controller can be (re)coded to provide either. Probably something like setting a recovery mode by depressing both buttons and the coded combination being sequenced to the LEDs. This was NOT considered for this submittal. Controllers are 'lovely' parts..the possibilities go on and on.
I appreciate that there are lots of solutions to this function. Some are more or less fun and interesting. For gadget freaks there is also the 'cool' factor to be considered.
Truchard will be presented the award at the 2014 Golden Mousetrap Awards ceremony during the co-located events Pacific Design & Manufacturing, MD&M West, WestPack, PLASTEC West, Electronics West, ATX West, and AeroCon.
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