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I thought this might be of interest to some people I have not seen this one before, it is an old design pin pointer with some advanced design features including a temperature stabilized front end oscillator, I have not built it but looks interesting.
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There's definitely some work gone into the design. These days, it would be sensible to replace the differential pair with an SMD dual transistor, which are dirt cheap. Back in 1989 , there wasn't much choice, dual transistors were expensive niche components.
The 'soft' power switching is an interesting feature.
It's nice to see a design that doesn't have more preset pots than fixed resistors. -
13 years ago, Carl M. said that he had permission from Andy Flind to publish this article/design , he just hadn't got round to it ...
Any chance a decent quality PDF of it could be added to the 'projects' page of the forum, Carl ?Comment
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I am about to build this one will post a vid when it is done I changed the audio output stage a bit and redesigned the board its much more compact now will keep you posted.Comment
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There's definitely a few improvements/changes could be made, using newer tech. The 78L05 could be replaced with a lower quiescent current equivalent, to reduce power drain. There's scope to make it run on two Lithium cells, as long as the 5V regulator keeps working, the rest of the circuit should be fine. A schottky diode for D3 (in series with the battery) would improve low voltage operation.
I would choose to put two LED's in parallel, and have one on the rear of the case, one on the front. When you're using it down in a hole, you need a rear LED. Using modern high efficiency LED's will get round the reduced current draw. Or .. use an additional transistor , one to drive the beeper, one to drive two LED's in series ... more efficient.
It would be good if it could be made to work at a lower frequency, like 30kHz, which is more appropriate for the typical targets we find.Comment
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What transistors are you going with ?Comment
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I am using BC549C for the NPN I have a lot of them, the BC184L is nothing special has a simillar gain 450-900 to the BC549C gain 420-800 see how it goes can always change them if i have to.Comment
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Here is a link to the pdf of the magazine this project is published in. Everyday Electronics, Sept 1989.
https://www.americanradiohistory.com...cs-1989-09.pdfComment
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Cool article on the pinpointer. The author did however violate the first commandment of DIY building: Test each subsystem before adding more parts.Originally posted by Skippy View Post
TESTING When the coil has been wound, the p.c.b. can be tested. The author has built quite a number of these units, testing being limited to simply powering up the complete p.c.b.'s and dealing with faults as they arose.
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Anyone built it. How about you dom44? Did you ever get around to building it and what was the result.Comment
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Here is the layout in Sprint. I've modified it for radial elecrtrolytic caps instead of axial, and some minor spacing adjustments.Comment
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haven't built it yet working on a PI detector and moded LOBO lite 30khz crystal locked and designing a 4069 3volt pin-pointer for specking small gold particles so far works not bad.Comment
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I see the 'American Radio History' site has a new name, 'World Radio History' , so I've updated the link to the pdf of this EE magazine issue:
https://worldradiohistory.com/UK/Eve...cs-1989-09.pdfComment
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Beta matching on a cheapo multimeter should suffice for the transistor pair. A vibro motor salvaged from old phone might be a good modification.Comment
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