Sadly, driving from Oop Norf to the top end of the South West is not currently permitted at the moment.
Bugger!..:roll:
You beat me to it, Minx…Foxy was the first thing I thought of when I saw that in the news! 
I can think of all sorts of responses I could give to that comment, but do not wish to get myself banned from this forum. :twisted:
A small ‘hickup’ has occurred with the metal detector…I say ‘Hickup’ more of a teething problem really…
I have been testing it out looking for old roman coins on my lawn ‘As you do’ and I found that the longer that I used the device, the more adjustment it needed, until finally after several minutes I ran out of adjustment. I concluded that it must be the load on such a small battery (PP3) was gradually running the battery flat. This was confirmed by a quick check of the battery, which was found to be low on charge after very little use.
I connected six AA batteries in series to produce the 9 volts required to power the machine and continued my search of the garden. After several minutes of operation, and no roman coins, I had once again run out of adjustment…
Plan ‘B’…I realised that something was getting warm…A resistor that gets warm diminishes its ability to resist and the result would be a continual need to adjust. Also, Some of the resistors required for the circuit did specify a particular wattage, of which I did observe in most cases but not all…There were two resistors of the same value (68k ohms 2 watt) that I was unable to source, so I used two 68k ones from my extensive collection, but sadly they might not have been 2 watt versions.
So with the unit operational I delved around with a probe from a digital thermometer. I did manage to find a resistor that had increased in temperature by one degree C, but it was not the suspect resistors, and all other components seemed to be stable. So later on I will add a makeshift heatsink to the suspect component and see what happens…Happy Days…
Well you seem to have it all in hand, OGF. I’m sure you’ll sort it out and I wish you the best of luck.
In addition to a heatsink, how about a small fan as well?
Thanks JB, but we must consider weight and battery consumption…
Surely the simplest solution for a big strong lad like you is to strap a car battery, or better yet a leisure battery to your back. 
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…
Once you get it fired up, Foxy…come and find the hidden gold in the Highlands ala Garnet Frost
Is this the future…Frightening or what…:shock:
Blimey that’s a bit weird. Surely the fright of seeing something like that would make you cluster together? :shock:
I’ll have nightmares about that now, Bob!
I take it that this is your next project, OGF! 
Notice the runner took no notice Pixie…
We don’t scare easily…:roll:
Sorry Mags, just think how scary it will be when a driverless car passes you on the motorway…:shock:
Now that’s an idea JB…
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
If he has a bag-load of treasure, he can afford to ditch the battery, or 'phone for a chauffer to come and collect the thing.
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.
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. :surprised:
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…:shock:
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…:-p
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…