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Hi All
This is my first post here, so apologies if the quality of the info is not up to scratch :-)
I've been looking about for a pinpointer probe that was fully automatic, and wouldn't break the bank.
Sadly, I couldn't find anything that was fully automatic (like the Garrett pro pointer) - no pots or adjustments, so have resorted to rolling my own. I had a good look through the forums before posting but didn't find anything.
This project is nothing original really, just a fairly standard colpitt's oscillator strapped to a picaxe microprocessor (picaxe is programmed in basic). I've used various flavours of picaxe over the years and like the easy way you can quickly lash up a project without resorting to buying a full blown development system (you can get up and running easily with their USB in-circuit adaptor - or make your own - http://www.picaxe.com). Above all, the picaxe is cheap (I mean REALLY cheap, the 08 device is only 1.80 GBP!)
At boot-up, the processor measures the oscillator frequency and stores its 'calibrated' value (it counts the number of oscillator pulses in a fixed gate time). If metal is detected, the oscillator changes frequency then if it's over a threshold value, it beeps - that's essentially it. No bells or whistles, it doesn't monitor battery voltage, light LEDs, tweet the results, record it's GPS location or flash a big light in the hole.
Sensitivity is about 20 to 25mm on a UK penny (about the size of a US cent) - I would have like a wee bit more, but this is fine.
I struggled to find a decent enclosure for the electronics, so ended up rolling my own again. The box is just layers of 3mm scrap perspex stuck together - again, not original - I cut all the layers one evening with a fretsaw and file (that would be sad, I have a laser cutter that I built :-) I also cut a foam gasket that seals the lid - the hole for the piezo sound is masked with some mylar film stuck to the back.
I've attached a couple of pix of the project, the source code for the picaxe and a rough schematic - no PCB, it's easily done on veroboard - if anyone wants to produce a PCB, feel free !
I'd be interested in anyone's thoughts on increasing sensitivity.
Cheers
Neil
PS I would have attached all the relevant info, but it seems I am not allowed to send attachments - do you require a first post ?
This is my first post here, so apologies if the quality of the info is not up to scratch :-)
I've been looking about for a pinpointer probe that was fully automatic, and wouldn't break the bank.
Sadly, I couldn't find anything that was fully automatic (like the Garrett pro pointer) - no pots or adjustments, so have resorted to rolling my own. I had a good look through the forums before posting but didn't find anything.
This project is nothing original really, just a fairly standard colpitt's oscillator strapped to a picaxe microprocessor (picaxe is programmed in basic). I've used various flavours of picaxe over the years and like the easy way you can quickly lash up a project without resorting to buying a full blown development system (you can get up and running easily with their USB in-circuit adaptor - or make your own - http://www.picaxe.com). Above all, the picaxe is cheap (I mean REALLY cheap, the 08 device is only 1.80 GBP!)
At boot-up, the processor measures the oscillator frequency and stores its 'calibrated' value (it counts the number of oscillator pulses in a fixed gate time). If metal is detected, the oscillator changes frequency then if it's over a threshold value, it beeps - that's essentially it. No bells or whistles, it doesn't monitor battery voltage, light LEDs, tweet the results, record it's GPS location or flash a big light in the hole.
Sensitivity is about 20 to 25mm on a UK penny (about the size of a US cent) - I would have like a wee bit more, but this is fine.
I struggled to find a decent enclosure for the electronics, so ended up rolling my own again. The box is just layers of 3mm scrap perspex stuck together - again, not original - I cut all the layers one evening with a fretsaw and file (that would be sad, I have a laser cutter that I built :-) I also cut a foam gasket that seals the lid - the hole for the piezo sound is masked with some mylar film stuck to the back.
I've attached a couple of pix of the project, the source code for the picaxe and a rough schematic - no PCB, it's easily done on veroboard - if anyone wants to produce a PCB, feel free !
I'd be interested in anyone's thoughts on increasing sensitivity.
Cheers
Neil
PS I would have attached all the relevant info, but it seems I am not allowed to send attachments - do you require a first post ?
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