I have to get started, here's with what

[Mikebits]

Geologically speaking, Africa is very wealthy.

 

[DMW]

back on topic

would it not be best to try and make a sortof constant current source?
i mean .2mm wire would have resistance of around .0218 ohms / meter, no idea how much your using but thats about 5.45 ohms at 250 meters of wire, and thus at 5V around 1 amp.

The previous document suggested a current of 40mA was only required, could you not be doing abit of "over kill"?, esp as if you have a properly balanced needle there shouldn't be [in theory] any other unwanted forces trying to turn the needle..?


EDIT

rereading through the link i posted earlier:
**broken link removed**
"The picture below is PIC-based air-core driver that makes use of an H-bridge power driver to feed sine and cosine weighted pulses to the movement's stator coils. The PIC interfaces to a PC serial com port."

he has several other surgestions for powering it too

 

[arrie]

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.

 

[DMW]

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 .

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]

:/

 

[arrie]

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.

 

[Mikebits]

Thanks mikebits, I'm aware of that, it's the Phillips chip solution, hard to get here in SA, but it uses two IC's.

If you like, I can order it here and ship it to ya
You sure it is two chip? Maybe I need to read better.
**broken link removed**

 

[DMW]

I wouldent bother, if you have a uC with analouge output then put that in series with the coil and in series with a resistor.

so that when it outputs 5V current is limited to 40mA, and thus anywhere between - and 5 volts means 0 and 40mA.

**broken link removed**

i.e. R1 = V/I = (5-.4) / .04 = 115 ohms,
at 2.7V out I = 2.7-.4 / 115 = 20mA
etc

Or just use PWM

 

[arrie]

If you like, I can order it here and ship it to ya
You sure it is two chip? Maybe I need to read better.
**broken link removed**

Sorry, I went to look up on myself, I was under the impression you required another IC in conjunction with this, alzheimer moment, Phillips just recommends using it with 87C751 mcu.
I suppose one can understand them promoting their own mcu as best to drive it with.
Anything should really do.

Thanks for the offer Mikebits. I'll go online and see if I can maybe get samples on-line or for that matter purchase is on-line.
Otherwise I'll let you know.

I bought my DAC08's yesterday as well. Funny story happened yesterday.
So I chose this supplier because they are close to where I'm picking up the laptop. They ended up not having stock, so I had to drive to the other supplier. Now the place where I wanted to buy it charged me R37.15 for the component. I thought to myself, that's not to bad, then I arrived at the other supplier, R10.
That's almost 1/4 the price.
I bought four, but either the one is really crap, or the first place is really ripping you off.

 

[Mikebits]

Otherwise I'll let you know.

Let me know anytime, whether it be that chip or any other. I am always glad to help

The internet has shrunk the planet. You are now a neighbor, and you know my take on that...

 

[arrie]

Thanks DMW.
I'll also look into the H-bridge configuration.
I haven't really played with the h-bridge configuration before, what's your timing requirement for the HB1 and HB2 connections from the mcu?
You might see what I'm getting at later with that question.
PWM could cause a slight shiver on the needle, if you get what I mean.
I would be a bit weary of driving it directly from an mcu for the sake of not sourcing too much current accidentally and damaging it.

I could be sounding a bit stupid here, but I'm generally very cautious.

 

[DMW]

R1 should stop too much current, tho now thinking about it youd probably not source enough current, maybe 25mA max not 40

well best thing with PWM is to try and see if it works or not, if you use PWM out form a uC it will easily do it in the kilohertz range up to Mhz.

 

[arrie]

Thanks Mikebits,will let you know.
Thanks DMW.

One bit of a setback, when I got home the magnet did not have a hole in it, so either I'll have to go and get the correct magnet, or get one somewhere else, or make a kind of a holder fitted to the shaft, but that seams quite a bit of work if to be done by hand.
I've also contemplated drilling a hole in it, but know that magnets are normally very brittle, so that probably will not work either.
These are alcomax 3 type.
I should have taken them out the packet and checked them. Dooh.

 

[Mikebits]

If you have a drill press with a slow speed, lots of oil and a uber sharp bit, you might be able to put a hole in it. Is it one of those fridge type magnets with the crappy rubber like construction? Use a drill bit that has a shallow first bite.

Also, you might be able to make your own magnet by storing a piece of steel on a beefy magnet for a period of time, in which case making a hole would be simple.

 

[arrie]

Thanks Mikebits.

I have a rather beefy drill press, but I'm sure I'll destroy more magnets than what I'll create successful holed ones.
I'm already looking at sourcing new ones. As I have to drive into Pretoria today, about 50km away, I'll make it another trip and go get some more somewhere.

 

[DMW]

you know what might be easier?

to go down a scrap yard a pick up an old dashboard, you could get one with 4 - speed, rpm, fuel, oil temp

if you dont use the whole aircoil and circuitry you could disassemble for magnet / parts

probs alot cheaper too

edit:
havent had a proper look but before this post closes and i doubble post

**broken link removed**

or from:
**broken link removed**
"Of particular interest are the rare earth cylindrical magnets which are magnetized through the diameter and have axial holes. That sort of geometry makes building the movement much easier."

 

[SPDCHK]

Sorry, I went to look up on myself, I was under the impression you required another IC in conjunction with this, alzheimer moment, Phillips just recommends using it with 87C751 mcu.
I suppose one can understand them promoting their own mcu as best to drive it with.
Anything should really do.

Thanks for the offer Mikebits. I'll go online and see if I can maybe get samples on-line or for that matter purchase is on-line.
Otherwise I'll let you know.

I bought my DAC08's yesterday as well. Funny story happened yesterday.
So I chose this supplier because they are close to where I'm picking up the laptop. They ended up not having stock, so I had to drive to the other supplier. Now the place where I wanted to buy it charged me R37.15 for the component. I thought to myself, that's not to bad, then I arrived at the other supplier, R10.
That's almost 1/4 the price.
I bought four, but either the one is really crap, or the first place is really ripping you off.

Arrie, as a fellow South African, Which stores are these that you are referring to? (I don't want to make the same mistakes)

 

[arrie]

SPDCHK,

the first one was RS in Kyalami.
Now I know everyone knows they are a bit expensive from time to time.
But I really wanted to limit my travels.
The place I got it the second time round was Communica.
Another place where components are cheap, but you probably have to place bulkish orders is Arrow Altech.
They are in jetpark.

DMW, thanks, will try that.
The thing is most circular magnet are TM. For air-core you need it at opposite ends with the mounting hole between the poles, opposed to the mounting hole going through both poles.

 

[DMW]

yeah, might be worth trying to contact mike at mikesflightdeck and ask him his suppliers tho hes probably USA

 

[arrie]

Yes, I think you're right, I generally don't mind ordering things from overseas if the store is big and reputable, but with income tax these days and the "greater" rand value, that can get a bit tricky.
I've spend numerous e-mails trying to explain the difference between through magnetisation and poles-on-ends type to the, you've guessed it, suppliers of magnets, as some seems to believe that the TM disk type neo. magnets will work just fine for my app.
Hallo. Can my fellow country men(woman) please go a have some very strong coffee.
No..... that might be a bit light.
Maybe they must go and lie in front of the wheels of an iron ore truck, that should work better.

 

[DMW]

Here i made an image for you, send them this

**broken link removed**