Digi-Key TechXchange Communities: Message List

Re: 230v water heater element control

noreply@digikey.com — Thu, 09 May 2013 14:43:18 GMT

A simple design is shown at www.electroniccircuits.com/electronic-circuits/filament-light-dimmer-circuit. This uses a DB3 diac to trigger a triac. The triac shown has a 4 amp rating, but you should use a 16A or 25A or 40A triac (depending on your heater element resistance) with an 800V rating for a 230vac supply (Digikey lists several triacs that will work). A similar circuit is also shown in the Fairchild data sheet for the DB3. Of course, the incandescent light bulb shown in the circuit is replaced by the heating element.

230v water heater element control

noreply@digikey.com — Wed, 08 May 2013 20:40:19 GMT

A variac is a very expensive option for a water heater, which probably takes 10 amps or more. A better idea is to use a triac with a simple control circuit, which applies ac to the element for a part of each cycle, depending on a pot setting (for example). This is like a light dimmer (for an incandescent light) but at 230vac and much higher current.

I.C. Help

noreply@digikey.com — Thu, 04 Apr 2013 13:33:13 GMT

It could be a standard dual op amp (LM2904, LMC6482, etc.) being used as a dual comparator. If pin 2 is biased so that it is normally higher than pin 3, then closing the switch will take pins 1,5,6 & 7 high, the collector of the 2N3904 low, thus applying a voltage near ground to the low side of the relay coil. The second op amp is connected as a unity gain amplifier and takes the hi end of the relay coil hi, so the relay and the led turn on.

Controller for reservoir sluice gate

noreply@digikey.com — Wed, 03 Apr 2013 14:06:21 GMT

While the commercial logic controllers are nice units for the price, few of them have sufficient output current ratings to drive the sluice gate motors, and most of them do not have enough inputs for all the sensors and limit switches. The outputs would have to drive additional contactors or SS relays, meaning additional cost and all the headaches of contact arcing if mechanical contactors are used. These are the reasons I recommended a "homemade" controller that would require more effort but would have a much lower cost.

Reservoir sluice gate controller

noreply@digikey.com — Tue, 12 Mar 2013 19:47:59 GMT

Hi Cecil,

You will need a DIP ZIF socket for your programming fixture like Digikey 3M4006-ND (not the one you ordered).

You will also need a 6 pin header (Digikey A26550-ND) to connect the PicKit3 to this socket. The fixture can be built on a vectorbord (Digikey V2011-ND). Cut off a small part with a bandsaw or shear and use the larger piece for the controller prototype. Small gauge solid wire like Digikey V1087-ND is good for wiring. Tools needed will include wire strippers, small diagonal cutters, needle nose pliers, soldering iron, solder, etc.

After it is programmed in the fixture, the processor will be placed in a socket (Digikey A94140-ND) on the prototype board. You will need 5VDC for the processor which you can get from the 120 VAC source using Digikey 102-2386-ND. I assume the limit switches in the actuators and the float switch will be at some distance from the controller, so it is highly recommended that the processor inputs be isolated from the cruel world using optoisolators. As far as I can make out, you intend to run 4 actuators, each having 5 limit switches. Optoisolators like Digikey H11L2M-ND should work for this, and there is a price break at 25 pieces. All chips in the design phase should be put on sockets; good sockets for the optoisolators are Digikey AE10021-ND. Finally, (and this is the major parts cost), the AC to the actuators need to be switched, preferably using solid-state relays like Digikey CC1080-ND. These are good for 25A which shold give you a good safety margin in case of actuator problems. I think you need 8 relays for 4 actuators, and there is a price break at 10 (a couple of spares wouldn't hurt).

I have made a preliminary framework for the processor program and am attaching it. Also attached is a drawing of how the processor should be wired to the other parts.

Reservoir sluice gate controller

noreply@digikey.com — Mon, 11 Mar 2013 21:52:42 GMT

After looking over the actuator specs, it appears you need 2 relays per actuator, one for clockwise and another for counterclockwise. Each actuator has a limit switch and a torque switch for each direction, as well as a thermoswitch.

With this many I/O, a PIC16F887 processor should be used (same as '886, but more I/O). To program these yourself, you need something like the PicKit3 (Digikey PG164130-ND, $44.95) with a 6 pin header (0.1" pitch) and a socket on a Vectorbord. If you do much programming, a ZIF socket is a good investment. The PicKit3 is run by Microchip's MPLAB, a free download. I write programs in Assembler (the One True Language) for these processors. It takes a while to learn Microchip's assembler language, but I would be happy to help you get started. The source code file (written in assembler) is processed by utilities in MPLAB to generate a Hex file, and PicKit3 writes the Hex file to the processor using its ICSP (in circuit serial programming) interface.

Reservoir sluice gate controller

noreply@digikey.com — Mon, 11 Mar 2013 17:09:06 GMT

Intriging. I would build this controller using a PIC16F886 microprocessor (about $2 for a LOT of capability) and solid-state relays for the gate actuators. It appears you have 4 actuators, or perhaps 8 if there is a separate circuit for raising or lowering. The relays can be controlled directly by the processor outputs. You have to know the current drawn by the actuators to pick relays that can handle the current. You might consider a solid-state pressure sensor instead of a float switch. This would feed an A/D input on the processor. The PIC16F886 is fairly easy to program (I could do it for you) and has built-in timers. It takes a +5V power supply; A 120VAC to +5VDC would cost around $20. As far as setting up the controller, it could be very simple if all the parameters are programmed into the processor, but then you would need to re-program the processor if you ever wanted to change anything. It would be better to have a digital readout (also controlled by the processor) and several switches and pots so you could change parameters without reprogramming.

update

noreply@digikey.com — Thu, 21 Feb 2013 18:37:34 GMT

See attachment

coordinates using angles from a tilt sensor SCL 1700-D01

noreply@digikey.com — Tue, 12 Feb 2013 19:37:13 GMT

If the length of the side of the square is s let r=s/2. Denote the four corners by A,B,C,D. When untilted, the (Cartesian) coordinates of the four corners are:

A: x=r, y=r, z=0; B: x= -r, y=r, z=0; C: x= -r, y= -r, z=0; D: x=r,y= -r, z=0.

If the platform is rotated around the x axis by angle u so as to increase the z value for A and B and decrease z for C and D, the new coordinates are A: x=r, y=r cos u, z=r sin u; B: x= -r, y=r cos u, z= r sin u; C: x= -r, y= -r cos u, z= -r sin u; D: x=r, y= -r cos u, z= -r sin u. The x values are unchanged since rotation around the x axis keeps a point at the same distance from the yz plane, and this distance is the x coordinate. Now rotate around the y axis by angle v to increase the z value for point A. This is the original y axis, not the line through the center of the platform that is the projection of the y axis. It is assumed that the x tilt sensor does not detect this rotation. Similar to the previous rotation, the y values do not change, so the x and y values for the points are now

A: x=r cos v, y=r cos u; B: x= -r cos v, y=r cos u; C: x= -r cos v, y= -r cos u; D: x=r cos v, y= -r cos u. But what are the z values? It appears easiest to use the fact that the four points are on a sphere with radius R=r times the square root of 2. Then z=square root of (R^2-x^2-y^2) (where the caret denotes exponentiation) gives the z coordinate of each point, remembering to use the appropriate sign of the square root.

Re: Followup - original and DUT.

noreply@digikey.com — Mon, 04 Feb 2013 15:26:17 GMT

Putting the LED and its series resistor between the 5.1v reference and the n FET drain is OK, if you don't mind the fact that the LED indicates that the p FET is getting a turn-on signal, not that there is actually voltage on the output. So if the output is shorted to ground, or the p FET is burned out, the LED will still light. A typical LED has about 1.2v voltage drop, leaving 3.9V across the resistor, so for a typical LED current of 10ma the resistor should be 390 ohms.

You could put another LED and series resistor across the 5.1V Zener diode to indicate that power is available at the input.

I'm not sure what you mean by bipolar load. If you mean that you want to pass a negative input voltage to the output, the present circuit will not work. Not only do you not get the 5.1V to supply the logic, but the output FET drive voltage is wrong. For an enhancement mode p FET, the gate voltage must be sufficiently more negative than the source to turn on.

As for Zener diode protection on the FET gate, most FETs will withstand 20V (some even 30V) of either polarity between the gate and source. If this limit may be exceeded, you will need a Zener diode between gate and source and a resistor in series with the gate to limit the Zener diode current.