14-03-2021, 10:53 PM
311
Re: Foxy's Latest Project.
Is this the future.......Frightening or what.....
https://twitter.com/i/status/1258797162684653568
14-03-2021, 11:15 PM
313
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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Is this the future.......Frightening or what.....https://twitter.com/i/status/1258797162684653568
14-03-2021, 11:56 PM
314
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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Is this the future.......Frightening or what.....https://twitter.com/i/status/1258797162684653568
15-03-2021, 10:02 PM
315
Re: Foxy's Latest Project.
Originally Posted by Pixie Knuckles
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Blimey that's a bit weird. Surely the fright of seeing something like that would make you cluster together?
We don't scare easily........
15-03-2021, 10:03 PM
316
Re: Foxy's Latest Project.
Originally Posted by Mags
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I'll have nightmares about that now, Bob!
15-03-2021, 10:06 PM
317
Re: Foxy's Latest Project.
Originally Posted by JBR
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I take it that this is your next project, OGF!
16-03-2021, 09:00 AM
318
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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Thanks for the compliment (I think..
) Fruitcake, I had actually considered carrying a rucksack with a larger power supply should the device be power hungry, or I was intending to spend long hours searching for the Yorkshire Hoard...But the jury is still out on both.Incidentally, the heat sink on the resistor made no difference, so we move into plan 'C'.....
Increasing the size of the control potentiometer....
16-03-2021, 09:58 AM
319
Re: Foxy's Latest Project.
Originally Posted by Minx
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Yeh, thing is, if you fill that rucksack up with the battery then how are you going to haul all that treasure that you uncover
Foxy, I don't know if you are interested, or if you have access to Sky TV, but a new series of River Hunters is due to start on the History channel on the 5th of April.
Two guys go rummaging around riverbeds in historical places such as next to a castle or an ancient river crossing using small pointer detectors. They have found all sorts of things including a Bronze Age axe-head.
Series 1 is also available on catch up.
16-03-2021, 12:11 PM
320
Re: Foxy's Latest Project.
If you are of a sensitive disposition, get bored easily, or have a short attention span....Look away now......It's going to get technical.... And I'll try to address Minx and Fruitcake's concerns while I'm at it....Not happy with altering the value of the potentiometer, I decided to continue down the route of the heating up of the resistor affair...
A good way to have a visual look inside an electronic circuit is to connect a milliamp meter in series with the battery and study the varying power consumption. It would certainly tell if the circuit was experiencing 'Thermal Runaway'....
The milliamp meter showed an ambient consumption of 21.7 mA...But continued to rise after a short period of time to 23.5 mA. This rise in current required adjustment of the potentiometer which brought the consumption back to 21.7 mA. Over the period of ten or fifteen minutes the consumption had risen so much that there was no longer any more adjustment on the potentiometer, and I was no longer able to stabilise the circuit.
What to do....?
It was obvious that 'thermal runaway' was the culprit, but after the heatsink failed to show any results I removed the circuit board from the unit, and replaced the 680k ohm ( what should have been a 2 watt resistor) with three large resistors (the only heavy duty ones I had) in series, and making up the 680k ohms required. A bit untidy, but practical......
After reassembly of the unit, it was ready to test.
I ran the unit under lab conditions for several minutes, where an initial rise in consumption was counteracted by adjustment, until it stabilised. Good news, it maintained the 21.7 mA for over twenty minutes, and following a search of the front and rear lawns, did not require further adjustment of the potentiometer. No gold coins though....
It had passed it's test with flying colours using the inbuilt 8 ohm speaker, however, when I repeated the test around the garden using the headphones the sensitivity became meteoric! and I found a few anomalies that had laid undiscovered while using the speaker.
Some underground cables connecting the summerhouse to the garage, and even some metal shuttering I had used while concreting the drive.....
So it's all systems go folks.......
Minx! Even with a fully operating metal detector I'm not expecting to exceed the remaining space in my rucksack with artifacts....
I must point out also, that with an ambient current of 21.7 mA, six AA batteries should be quite sufficient for a days detecting. But I admire your optimism....
Fruitcake! Unfortunately (or fortunately as the case may be) I don't have any access to Sky. The only dish in my house is the one that I eat my porridge out of....
I watch very little TV, I find it terribly counter productive, however....After suffering a couple of heart attacks I tend to get very tired in the evenings, and pretending to watch TV while resting stops Mrs Fox from worrying and getting concerned about my health....
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