I'm starting a little project that will run a square wave through a copper coil to make magnetic pulses. I imagine the project would be quite straight forward if I were a little more experienced with making electronics.
The exact specifications of the coil and magnetic pulses are essentially not that important. I don't want to go into too many details about why, but suffice it to say the device should "work", i.e. it should generate magnetic pulses that are easily detectable with, say, a steel washer. The frequency range I'm targeting is about 50-120Hz which I'll generate with the PWM module in the PIC.
Here is what I have so far:
I'll use a 2155 type 1A xformer, and I'll be using the 6.3 and 15V taps.
I'll use the 6.3V to drive a 5V VR to power a PIC16F877A (I think those are the ones I alread have lying around). The PIC will use a potentiometer set up as a voltage divider on an analog pin to control the frequency between a given range (I've never done any analog or ADC stuff before). The PIC will also drive a small 8-segment display to show the frequency, and I'll use a crystal oscillator to give the PIC a more stable clock (I've had issues with timing in PICs before). The square wave will be between 0 and 5V.
For the coil, I basically want as much as possible, so I'll use the 15V to drive a 12V VR. I'll use the square wave output of the PIC (positive only) as a 5V input to an OpAmp. 5V -> 12V is a gain of 2.4, so I'll use a 240K and 100K resistor for the feedback of the OpAmp (I've also never used an OpAmp before either). I'll also use a schotky diode, reversed, to prevent the collapsing field to burn anything out.
I hope that all makes sense and sounds more-or-less reasonable. I know I don't need to use a PIC, but I've used them before and they're easy to program use, and I'm a lot less confident doing analog frequency adjustment with, say, a 555 (also never used these before either, lol), and using an 8-segment driver. I just want something that works and that's within my capabilities.
Here are some parts I have so far: (I'll be using 240V mains)
- 2155 type 1A transformer with 6.3, 7.5, 8.5, 9.5, 12.6, and 15V taps.
- 7805T 5V regulator
- 7812T 12V regulator
- BR104 10A 400V rectifier x2 (one for the 6.3 and one for the 15V)
- 8Mhz crystal for the PIC
- 1K linear VCU pot
- SB560 schottky diode 60V 5A
- 0.5mm 500g enamelled copper wire (approx 180m length)
I'll also have some electrolytic caps before and ceramic caps after the rectifiers in the power supply sections. I've got a bunch of these lying around in my drawer already.
I have a few questions:
- If I've said anything absurd so far, please point it out.
- Let me know if any of these components seem wildly overkill, e.g. the schottky diode or rectifier, for example.
- I'm not sure if I even need a voltage regulator for the high(er) voltage section. If I can avoid it and just use bigger caps, I can drive the coil at 15V which would be "better".
- I have no idea what OpAmp to get. I'm looking at the LM301AN which seems reasonable.
- I'll wrap the coil reasonably tight. It's ~180m and I aim to have it in a small package around 4x4x2cm approx. I don't know how many turns this will be, but probably "a lot". I can only assume that driving a 0.5mm copper coil at 15V @ 120hz should be fine? (i.e. won't burn out)
Sorry for being so vague. If you comment with a question I can actually answer, I'll do so.
Thanks for your help.
If I get some things clarified here, I'll order the parts online and post a circuit diagram in the next few days, and then we can all laugh together at how bad it is.