Bill E.

I haven't seen any responses to this post by TKOTC since Aug. 17. I hope you are allright? I am always worried when someone wants to start using the mains AC power from a wall outlet in a project. Call me a worry-wort! I have a relative who is building a "device" that distills fermented stuff (whatever it may be!) into, for the sake of this post, "alternate fuel". Use your imagination and you can figure out what it is. He needed to control a water heater heating element, a 1500 to 3500 watt device, and was looking for advice. I did give him some - reluctantly. He is still with us!! There is available, on the web, a ton of posts about building a "device" for distilling fermented stuff. The majority talk about using a triac, a potentiometer, capacitors, lugs, etc. That is a good way to do it. The problem I had was the lack of warnings and cautions to the reader of getting their butt fried by 220VAC! Or 115VAC for that matter. There was very little warning of using an "isolated tab" triac, et al. So I send this advice with a degree of consternation. An SCR is an ideal device for the half-wave vibrator. You do, however, need a method to "remove" the electrical circuit in order to shut an SCR off. You cannot do it via the gate terminal. You will need an intermediate "switch", or equivalent, to do that. MOSFETs won't work like you think when switching AC. The IGBT is, for lack of arguement, nothing more than a power MOSFET with a bipolar transistor controlling its gate. You could use a triac followed by a rectifier (big enough to handle your load(s)) to run the vibrator. A triac can be turned on and off with its gate. Use the opto-isolator with the netduino. Please, PLEASE be careful!! I cannot scare you enough about working with mains. If you were an electrician, or a disciplined timkerer, well, then you know the way to do this and, possibly, how it feels to get knocked on your keester by mains voltage. But for a beginner, I am "discouraging" you to mess with this without having a CPR qualified partner nearby. I am SERIOUS about this! Mains AC is not to be fooled with! I am speaking from experiene. And, yes, I am CPR qualified. If anyone on this forum disagrees then you are: 1. Lucky 2. Never fooled with mains AC 3. An experienced Electrician that doesn't care about anyone else 4. Misinformed about the pain, physical mutilation, agony from electrical burns 5. Add your own description By itself, a Netduino cannot harm you. You can put your tounge on it and it will only (probably) stop working. No big deal. You won't feel a thing. Playing with high voltage (anything over 32 VAC/VDC is high voltage to me!) will bite you! Bad. And, you do NOT want to experience that. It takes less than (if I remember correctly) 8 ma of current to the heart to stop it. Your mains circuit breaker is normally 10 or 15 AMPS! Enough said. Be careful. BE CAREFUL!! I don't want to hear about anyone, eecially on this forum, being hurt by messing with something that they don't understand. I would like a similar post to ALL members warning about fooling around with household AC. Again, you do not know what you are dealng with if you are an amateur. Bad mojo. Ask a pro or a friend experienced with AC. PLEASE!! All my best regards, Bill

This reply has its roots in my post earlier about the Hardware guy having problems with the software side. I hope I can help out a little here. Let's see if I understand what you are after: you want to power a servo (a typical analog type), control it with a mini and power the mini from the same battery? All in all this is not so difficult but has its issues, as Mario clearly pointed out. Heat, heat, heat. You can power the mini right off of the 9V battery - no problem. The MC3392 regulator used on the mini can tolerate an absolute maximum of 20V so you have lots of headroom there. It will have some heat loss but it will be very little since the mini draws next to nothing in power. Now the servo is another matter. Some folks say, key word "say", that some servos can tolerate a 9V source for a short while. I would NOT recommend that. An elegant solution is to use a DC-DC converter like the one available at Digikey here: http://search.digike...1709-nd&stock=1 This device is over 90% effecient, needs no heatsink (no, or VERY LITTLE loss to heat) has a minimum input of 6.5V and has an output capable of up to 500ma. It is a drop-in replacement for the LM7805 part. And it is less than $8. I use these parts in my professional work. I love them. When I monitor the current supplied by my bench power supply and I stall a servo (not too easy to do!) I still draw less than 1/2A of current so the converter should do fine for your app. Another, more pricier one, is to use polymer-lithium batteries. For your app there woould be three in series (1.7V x 3 = 5.1V) for powering the mini off of pin 21 and your servo directly. If you use 4 in series (6.8V) you have enough overhead to power your mini via pin 24 and the servo off the same power source. That allows a small margin of isolation between the servo (very noisy electrically) and the mini. This would require a charger also. Check out Sparkfun. BTW, I ampowering my entire robot (3 servos, a mini on a Parallax Super Carrier) with 4 nickel-metal hydride batteries with no problem. That's only 4.8V. Hope this helps some. Regards.