Hi Ron H is that for 12 volts or 24 volts. Thanks to everyone.

That was for 24V. For 12V, use R2=27, R1=560. You still need something like BC639 or 2N2222 for Q1.
From a performance standpoint, you would be better off with a P-channel MOSFET for your high-current switch. It might be more difficult to obtain and/or cost a little more.

 

I would like to thank everyone for all your help on this it works brilliant. But would it be possible to use a hall effect switch instead of the reed switch if so can anyone explain how to go about it. Thanks Ron.

 

I would like to thank everyone for all your help on this it works brilliant. But would it be possible to use a hall effect switch instead of the reed switch if so can anyone explain how to go about it. Thanks Ron.

Can you use a surface mount part?

 

Yes surface mount would be ok but I would prefer to use something with legs if possible. Something like DN6848-ND or TL172. Thanks for replying.

 

Yes surface mount would be ok but I would prefer to use something with legs if possible. Something like DN6848-ND or TL172. Thanks for replying.

I can't find datasheets for either part. Can you provide them, or links to them?

 

Philco used to sell UGN3130's - they were a Hall-effect switch in a SIP case similar to a TO-92, only much thinner. Power, ground, and signal out. Put a small magnet behind it, and it would detect ferrous objects in front of it. Doesn't get much more simple than that.

Anyway, here's a search on Farnell's UK site. Came up with 20 3-pin SIP Hall-effect sensors that they have in stock.
Datasheets are available, parts are available.
http://uk.farnell.com/jsp/search/br...Ntt=hall+effect+switch&Ntx=&_requestid=205659

 

Sorry for not following convention in my circuit/schematics, I have come under fire for this before on this forum but I don’t have very good software (PCB wizard) and is very limited and out of date.
Can you please have a look at this for me and let me no if I’m just mad or will this work OK.

 

You'll need a pull-up resistor on the output of your HE sensor, as the o/p is open drain. If it were me, I'd add a collector resistor for Q1 as well.

 

Sorry for not following convention in my circuit/schematics, I have come under fire for this before on this forum but I don’t have very good software (PCB wizard) and is very limited and out of date.
Can you please have a look at this for me and let me no if I’m just mad or will this work OK.

I think you picked the right part, but with your circuit, it will invert the function of your magnet (when you add the pullup, as Thingmaker suggested). See the circuits below for some ideas that should work.
I added a couple of circuits using PMOS drivers, which would be much more efficient.

 

I suggest that your bypass capacitor across the Hall-Effect sensor should be closer to what's called for in the datasheet. Currently, it looks like you have a 1uF polarized capacitor in there. If it's a tantalum cap, that might be OK. An aluminum electrolytic cap would probably have too many parasitics to be effective enough.

I suggest changing it to a 0.1uF ceramic, tantalum or poly cap.

 

Thanks Ron H for the diagrams I’m going to try the mosfet ones and thanks to you SgtWookie for the heads up on the cap.

Sorry guys I have a question, will I need to change R1 to use the A3245EUA in my diagram or will I need to add or remove anything. Only all the parts have arrived today and I’m eager to put it all together.

Thanks to every one for your help.

 

Thanks Ron H for the diagrams I’m going to try the mosfet ones and thanks to you SgtWookie for the heads up on the cap.

Sorry guys I have a question, will I need to change R1 to use the A3245EUA in my diagram or will I need to add or remove anything. Only all the parts have arrived today and I’m eager to put it all together.

Thanks to every one for your help.

If you mean the 56 ohm resistor, it still needs to be 56 ohms. Otherwise, I would have changed it.
If that's not what you mean...
EDIT: If you mean the R1 (1k) in your latest schematic, that circuit will, as I pointed out, invert the function of your magnet (assuming you add a pullup to the A3245). The load will be driven when no magnet is near the A3245. It will not be driven when the magnet is nearby.

 

Help! I have put to gather all 4 of the circuits that Ron H posted. The 2 transistor ones work brilliant but at the time I ordered the parts for the 2 mosfet as well, postage pricing and all that. Now both of the mosfet circuits don’t work, if anyone as come across any of my old postings I may have mentioned I don’t like mosfets or they don’t like me and I avoid then like the plague every time I play with then nothing ever works. So it maybe my dreaded mosfet curse again. Any ideas please

 

Help! I have put to gather all 4 of the circuits that Ron H posted. The 2 transistor ones work brilliant but at the time I ordered the parts for the 2 mosfet as well, postage pricing and all that. Now both of the mosfet circuits don’t work, if anyone as come across any of my old postings I may have mentioned I don’t like mosfets or they don’t like me and I avoid then like the plague every time I play with then nothing ever works. So it maybe my dreaded mosfet curse again. Any ideas please

MOSFETS are very sensitive to ESD (electro-static discharge). You need to purchase an ESD wrist strap and prepare an ESD proof work station in which handle the devices and the resulting circuits that you build. This is common practice in the electronic's industry.

hgmjr

 

Thanks for the heads up but I am aware of this sensitive to ESD and I do have a complete electronics work and bench at my disposal. I ordered 20 of the fets knowing my history with fets. I have built the 24 volt one 3 times. One with an etched board, didn’t work, Vera board, didn’t work I then printed the diagram off as is then glued it to a board, banged some nails in and put it together as is, but still no look I used new parts for each build.

 

If your ESD precautions are not protecting the devices then you may need to look at the nature of the circuit. It may be that you are exceeding a device maximum without realizing it.

hgmjr

 

Ok, I’ve gone back started from scratch again. I have tried a load from 100 MA up to 2 A (Bulb) it still want light it not even a flicker. I have tested the fets and all OK. So all I can conclude is there has to be something wrong with the diagram but it all looks fine. I completely stumped. Thanks for your input on this.

 

Ron Roberts,
Could you take a digital photograph of a couple of your non-working examples and post them? We may spot something that you have overlooked.

Voltage readings at various points in the circuit would be most helpful in determining where the problem area lies.

 

sorry wrong diagram

 

Hi sorry for my delay away at work. I connect the 24v PSU the bulb lights strait away but very dimly. Please let me know ware you want me to take the reading. I will take pic of my completed board and post.

Sorry for my constant editing on this forum still working out the size for the pics.