hedgerows got the soldering iron out

[hedgerow pete]

well i have almost finished rebuilding this hadron colider again, blooming thing is a heap of scrap, get a new one i say but they dont listen!!!!

any way i am on the scrounge, does any of the local birmingham bee keepers have a small 12 volt dc electric fan knocking about in there sheds any where.

we are talking very small here about 40 to 50mm square will easily do it for me or does some one have on kicking about inside some thing say an old computer.

what i have built over the day is a small control board that will act as an incubator controler for the allotment,
i just want a little fans so it is not a still air incubator but a fanned air jobbie.

just went to maplins to get one and they want £7 just for the fan on its own, so i left , quickly!!!!

and lastly can all you techno intelligent people that realy do what this electronic stuff does , can you have a look at the shcematics below. i need to run the temp at 37.5 degrees.
using peters ***** guide will all i have to do is to replace the 100K potentimetre with a larger one for a slightly higher range.

i have scanned the older version but it came out very naff so aftyer looking at the old version the only differences i can see is that,
D2 1N4148 IS A WIRE LINK ONLY AND R3 IS A 40K OHM AND R7 HAS BECOME 15 OHM. he has still used the 100k pot and not changed itView attachment 3361

 

[Hombre]

Does any of the local birmingham bee keepers have a small 12 volt dc electric fan? About 40 to 50mm square.

just went to Maplins to get one and they want £7 just for the fan on its own, so i left , quickly!!!!

Can you have a look at the shcematics below. i need to run the temp at 37.5 degrees.
using peters i'diot guide will all i have to do is to replace the 100K potentiometer with a larger one for a slightly higher range.

D2 1N4148 IS A WIRE LINK ONLY AND R3 IS A 40K OHM AND R7 HAS BECOME 15 OHM. he has still used the 100k pot and not changed itView attachment 3361

Yes I have a small CPU fan that I replaced in a PC that runs 24/7 and has done so, except for holidays, for the last six years. So it's well tested and has had the crud brushed off a few times too.

PM me a telephone number and I'll call you this evening if that's OK. The fan is almost free of course. Three virtual sequins to you.

The going price for a new fan is unfortunately at around the Maplin price. You can find cheaper ones, but then are crippled by postal charges. Don't throw such things away is the best advice.

D1 is essential, it absorbs the back EMF when the current to the relay coil is switched off. Without it the junction of the transistor is apt to get destroyed, sooner or later. Big pulse!

R7 controls the gain of the opamp and R3 limits the current or sets the bias for the transistor.

Changing the potentiometer probably won't help an awful lot. Better to do something slightly different when you know where you need the knob set, perhaps to give you a finer control close to the temperature of interest.
I see that the IC is an LM324 and only half of it is actually being used.

D2 seems a bit weedy as an 1N4148 is a signal diode. I would have used something slightly beefier here, but if it works it's good. It should stop you doing the HP smoke test, but be advised that silicon diodes tend to fail short circuit, so if it does fail in normal use it becomes like a piece of wire and might allow you to power it up backwards without the protection you expected. I'm sure you woudn't do that though Pete? . . . Pete . . . ?

If you can manage to rescan just the schematic in more detail so that it isn't fluffy when I try to make it bigger, then it might be of use to others, without making them blind.

 

[Hombre]

D2 is good for 250mA at 75V, so is well within it's rating. The only difficult component is the 5.1V Zenner diode, because I don't have one.