GS 5 THRESHOLD PROBLEM

[kt315]

basics electronics school again DR? again just bad student with low motivation to learn something.

[daverave]

basics electronics school again DR? again just bad student with low motivation to learn something.

Hi kt315....i cannot understand why people cannot be frank and say what the solution maybe...there are people on here with knowledge but unwilling to help...its only you and a few others who are interested in helping....its not a matter of school cause some electronic problems can be very vague and unencountered before.

[Jose]

Maybe there is a problem in the regulated line of +5 volts, which falls abruptly. This would explain why the threshold goes out of range.

[daverave]

Maybe there is a problem in the regulated line of +5 volts, which falls abruptly. This would explain why the threshold goes out of range.

ive tested the +5v & -5v supplies and are stable when the supply voltage is reduced....the - 14v & -10v supplies change according to lower voltage levels...i may try and increase the -10 v to -12v so if i drop the supply voltage a couple of volts then in theory if that is the problem the threshold should not change.....if not i may have to change the -12v regulator on the audio pcb to a low drop out type....like most of us we are still learning about detectors and cannot know everything that raises its ugly head.

[Hyena]

If thershold is connected between +12 and - rail or GND (I do not have your schematics) and your battery drop under 14V, regulator become noisy and your threshold also.

[daverave]

If thershold is connected between +12 and - rail or GND (I do not have your schematics) and your battery drop under 14V, regulator become noisy and your threshold also.

on the GS 5 there is an adjustment for fine adjustment of the threshold level which has a -5v & +5v on each end of the potentiometer...the -5v & +5v supplies are stable even with the supply voltage down to -10 volts...its the -10v & -14v supplies cha nge according to supply voltage...i would have thought the GS 5 should operate down to maybe 11 volts without any problems but im only guessing.

[Hyena]

I always expect problems when I am under drop voltage of regulator Stable mean you already checked with scope in mV scale?

[dbanner]

Battery voltage needs to be kept healthy for device to function properly. The regulators need more juice.

[Jose]

Try a negative, low-drop regulator.
I use LM2991T.

[daverave]

Try a negative, low-drop regulator.
I use LM2991T.[ATTACH]44665[/ATTACH]

Hi jose....did you have the same problem with a GS 5 ????

[dbanner]

I think I saw 79L12 reg. as well for audio stage. You'd have to maybe change it too.
I wonder what the overall current consumption is like for the entire unit. Maybe you could rationalise the entire power supply for more time in the field. A good mod solution for entire unit, whilst keeping it lightweight.

[daverave]

I think I saw 79L12 reg. as well for audio stage. You'd have to maybe change it too.
I wonder what the overall current consumption is like for the entire unit. Maybe you could rationalise the entire power supply for more time in the field. A good mod solution for entire unit, whilst keeping it lightweight.

Hi dbanner...with my GS 5 the current consumption is around 650 mA cause i added a amplifier stage to boost the audio.

[dbanner]

Yeah well, you've got yourself a battery killer. Low dropout devices may not help as much as you'd like. Rechargeable batteries discharge curve I suspect is not too linear. It may go from 13v down to 10v a lot faster than say from 14.4v down to 13v (maybe exaggerated, but you get my meaning). You may only get a few minutes worth of extra hunting, that's not much at all. A combination of higher capacity battery and some more efficient linear devices is one way to go maybe.

[dbanner]

Nice low current audio booster can be had from old computer cd-rom drives, the audio chip and associated circuit is on small circuit board to the front along with headphone jack and volume control pot, all self contained. Easy hack

[daverave]

ive used li-ion batteries so should get about 4 hours running time which is ok for a normal search....the threshold problem is annoying as cannot zero (silence) below 13 volts supply....i only ever had this problem before with the surf pi and only if i used too much feedback on the dc amp.