Having fun with a PIC16F84A microcontroller

[ikoflexer]

I'm planning to use a PIC16F84A microcontroller to keep the shunt current within a certain range, in a shunt voltage regulator. The regulator I have in mind is the salas simplistic that can be found in this thread

The simplistic Salas low voltage shunt regulator

I've started to put together a page with some info about the pic chip, just in case other people might be interested.

The page is found at this link , and is very much work in progress.

More details to come, stay tuned.

[Tham]

Love to hear that I may soon be able to remove the big heatsink from the high current shunt regulator. Again I volunteer to build the first one .

[anatech]

Hi ikoflexer,
Thank you very much for this!!

I will be watching and reading. I do have a PIC16F84A on hand already.

-Chris

[jkeny]

Great start, Iko. Can you say anything about how this will work, what the concepts behind it are? However, I don't mean to start an endless stream of requests for functions, in fact, I believe it should be kept tight & minimal, especially as it will be a first uc project for lots of us

Thanks for kicking this off - I'm sure we'll see this thread mushroom into many pages

[jameshillj]

.... "pic" controlled, shunt reg, high current, power supply - grabs your attention - this's something 'right out da box' - definitely not so simple now!

Maybe a "Salas 'minI pic' shunt reg"!

Will follow, with interest - very far behind, unfortunately!

[ikoflexer]

Thank you guys.

Here's the spiel, and I'm just thinking out loud here. The pic I'm looking at has a total of 13 I/O bi-directional pins. We can set a few pins to be inputs, and a few to be outputs. Using some kind of a resistor ladder the input will be a simple A/D converter, converting the voltage across a resistor sensing the shunt current to a few zeros/ones which will be fed to the pic. The pic makes a decision to decrease or increase the shunt current, and it puts a code of zeros/ones on its output pins, which will now be converted by a simple DAC (can also be a resistor ladder thingy, maybe) to a voltage, used to increase/decrease the value of a voltage controlled resistor (mosfet?) which in turns controls the shunt current. I'd like to keep it as simple as possible.

[astouffer]

No need for a DAC or anything fancy. Look at the chips with PWM modules built in. Feed the PWM signal into a low pass RC filter and you'll see a DC voltage.

The PIC16F84 is a pretty limited. A 16F684 or 16F628A is a good starting point.

[ikoflexer]

Originally posted by astouffer
No need for a DAC or anything fancy. Look at the chips with PWM modules built in. Feed the PWM signal into a low pass RC filter and you'll see a DC voltage.

The PIC16F84 is a pretty limited. A 16F684 or 16F628A is a good starting point.

Thanks! I already looked at the 16f628a because it has an internal oscillator so, fewer outside parts. But didn't think to of using the pwm module. I was also considering the 16F716 which besides the pwm module has an A/D module too. This is all very new to me...

[Nigel Goodwin]

Originally Posted by ikoflexer

Thanks! I already looked at the 16f628a because it has an internal oscillator so, fewer outside parts. But didn't think to of using the pwm module. I was also considering the 16F716 which besides the pwm module has an A/D module too. This is all very new to me...

The 16F84 was obselete last century, replaced by the 16F628 - however, due to demand for an old part (why?) they reintroduced it at a higher price. You certainly shouldn't be using a 16F84 these days, and even worse not writing a tutorial using one, you're just prolonging people using it - use a modern device, cheaper, higher spec, and easier to use. The 16F84 is long dead, don't keep dragging it up.

For a regulator you really need (as a minimum) hardware PWM, and analogue inputs, this makes it trivial to make a regulator.

If you check the circuit and software for the PICKit2 (MicroChip programmer) they use hardware PWM and analogue feedback to create a 13V regulated supply from the 5V USB port voltage.