As you can see that was my first feeling too, I can then control the voltage output using a simple digital word from one of the PIC registers.
Match that to the input square wave, should work.
Or at least easily enough for the 150Hz input signal. but will need more than 8 bit word for 900Hz input.

I'll just have to choose the DAC carefully.

So, I've collected some copper wire, 0.2mm. That should work for my air core coils.
I'll be testing my coils to magnet effect manually at first using LM317 regs in adjustable configuration.
Will have to buy a suitable magnet, have found 20mm bar magnet that will be great. Not too expensive either.
If all is fine after manual testing I might use the DAC08 to control the voltage going to the air coils. Still have to do calculations regarding the vref to output ratio, but will do that after manual testing has fixed some of my parameters.
That's about the cheapest DAC I could get, but seem to have reasonable performance for my purpose.

I've officialy run out of HD space on my PC on Sunday, so that will make the 110+ km trip worth wile, will also get another HDD.

We do have a fair share of snakes.
Even the dreaded rinkhals have started popping up in the area, worst of it is it's not even supposed to be here.
We are also close to one of a very few breeding areas in Southern Africa for vultures.
If you hike up to the top of a mountain, they are actually flying around you.
Damn, those birds are quite big and scary, believe me, you end up watching you back all the time.
Other than that, you'll have to go to one of the close by game farms for the rest.

It's great visiting if you're from US or UK/Europe, the rand is a bit soggy, so holidays here are great value. That's is if you can stomach the air fares.
Just say when you want to come.

I think boomslang is closer to Jhb, heck he lives in one of the suburbs.
We're quite far from Zim, but in all honesty, most of Africa is in turmoil. The Zim illegals here are not really a problem, they want to come to work, more than what we can say about a large part of our own people.
The real trouble here are Nigerians.
They head up most of organised crime, drug smuggling, etc.
Crime cost the people of South Africa billions annually, but there seem no way of stemming the crime rate at this point.

These things tend to make one very negative, but I do not even want to list some stats.
This is one heck of a beautiful country, and for the most part, filled with lovely people, I've found some in almost all corners.
I've come to fall in love with the Eastern Cape, and would like to move somewhere there one day.

Don't worry MikeBits, it is relevant to life, and in the greater influences the whole planet.

I think Africa is in the crap it is in because of gross incompetence.
The guys at the top seems to be the only ones getting somewhere in most countries. That tells you immediately that the guy at the top is using the whole country for himself and his buddies. He should not be there.
I call them territorial pissers.
That is mainly why Africa is poor, because I think Africa is actually very rich, in terms of what is underneath its soil.

Enough politics for one day, besides I'm scared some of our alien friends might take this post over as well.

Thanks DMW.
That is very relevant, and I'll implement much of what is on that page.
Mikesflightdeck is really a cool site. Lots of really nifty pieces of information.

I will not be using such a lot of wire to start of with, but will keep some tabs on the results with different length of wire. I was hoping to get away with 35mA driving current per coil, so that will also determine the length of wire used for the coils.
Luckily my coils will be really small.
I have not yet bought my experiment components, as someone wants me to supply them a laptop. I'm finalising that deal, and getting everything in one trip. The bit of profit from the laptop deal will also be responsible for purchasing my components.
Good going on that site.

Couldn't post your results and construction methods? id be very interested, youve got me interested in air coils abit now, im considering making abit of a home-made clock with them :P.

Through id rather be certain on things before i commit to buy [surprisingly expensive] magnet wire, and other things;
such as why a H-Bridge will cost me around £4
when i can make one easily from 4 mosfets costing 25p each [total £1] or even for this current could use 4 cheap BJT transistors which will cost 7p each [total 28p]

:/

I'm fetching my components this morning, the laptop deal that kept me waiting came through, so I'm almost off.
I will let you know what happens.
The thing is to get real angle on your needle you actually also need negative polarity on each coil, but I will not need that much angle, so I believe I'll succeed with driving just positive voltage into both coils.
But as mentioned, I have to play with that concept first.
Will keep you posted.