My surf pi threshold is not steady,it pulses the speaker every second or so.The output of the preamp shows this as zero jumps around,it is not dead flat.Now garbage in garbage out right? The input of the preamp has voltage spikes on the rising edge of the tx pulse,the spikes are constantly moving in amplitude and go negative and positive.The same thing on the peak of the flyback. Now the input to the preamp is protected by the 4148 diodes and 1k resistor and the tops of the tx and flyback pulses are around 800mv tall,the voltage spikes are going above the tops considerably. Let me take some screen shots and show this,I have read several post's of people complaining the surf pi does not give smooth thresh,one guy described it as motor-boating. Do I have bad diodes or input resistor?
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Originally posted by porkluvr View PostIs your ICL7660 synchronized to the transmitter, or perhaps instead I suspect it's running just a few CPS higher or lower?
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Carl's right, that does look alot like RF or noise pickup.
On the subject of the diode, I think the diode is there simply to keep the input to the osc pin from being pulled above +5V that serves as the 7660 supply voltage, possibly causing damage.
I would think just about any diode should work if you wanted to try synchronizing - but - being as how you have let two different 7660 "free run" and still had problems, I now doubt that synchronization is the answer you are looking for.
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Or make another coil and twist it into a figure 8 shape and watch the CRO the noise should be reduced.
In that second picture if I'm reading the setting correctly it's showing a TX of 50us per div and the amp is taking 50+us to decay, if that is correct thats the reason for the poor sensitivity 50+us to decay is too slow. All the problems could be just the coil and the fact your inside with a lot of external EMI.
Mick
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Ok I will try all those suggestions,I think my scope runs on batteries also maybe I can take it out in the woods and check it,that would be *****in.Yes the tx is 50us, and yes it takes way too long to decay. And it has the 390 damp resistor in it now,and its still that long.I started out with a mosfet irf9520 100v,but I switched to the kit supplied irf9640 because its 200v and I wanted to see if letting the flyback go higher would get it to decay faster.I have seen it decay fast.And I have sampled at 15us with a 280uh/3ohms coil,and the 9520 mosfet.
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Originally posted by Carl-NC View PostThis looks like RF noise pickup to me. While looking at the preamp output, try rotating your coil around in different directions.
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hello brian,
just been reading this thread , all sounds very similar to a problem i had on a home made detector.
1Hz clock signal in the house , breaking threshhold as regular as clockwork so to speak.
i never did find the source , but went round house turning everything off , even took batterys out of electromechanical clocks.
only to say it never happened in the field .
you say turning the coil can help reduce noise , i even tried to locate source of noise using detector !!
my only conclusion was as i said 1Hz clock signal , but not from my house , poss from next door.
good luck finding yours.
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Originally posted by DOOLEY View Posthello brian,
just been reading this thread , all sounds very similar to a problem i had on a home made detector.
1Hz clock signal in the house , breaking threshhold as regular as clockwork so to speak.
i never did find the source , but went round house turning everything off , even took batterys out of electromechanical clocks.
only to say it never happened in the field .
you say turning the coil can help reduce noise , i even tried to locate source of noise using detector !!
my only conclusion was as i said 1Hz clock signal , but not from my house , poss from next door.
good luck finding yours.
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