SURF PI SHIELDING QUESTION

[daverave]

on the surf pi is the coax shield connected to the positive rail or to ground...its something that i have forgot (getting old) i may have to open up my surf pi detectors to check where ive connected the coax shield...cause sometimes they are a bit unstable on the beach.

[kt315]

easely to remember. if you see P-Channel MOS-FET - a shield is -BATT or 'ground'. for N-Channel one a shield is positive, +BATT.

[Qiaozhi]

on the surf pi is the coax shield connected to the positive rail or to ground...its something that i have forgot (getting old) i may have to open up my surf pi detectors to check where ive connected the coax shield...cause sometimes they are a bit unstable on the beach.

The Surf-PI should have the shield connected to GND (negative terminal of battery).

[daverave]

many thanks to both of you for your help....my machines seem a little unstable and thought it was earth's magnetic field and was not that so maybe i got shield connection wrong so will have to check it...when i was on the beach the other day one of my surf pi detectors stopped working after bobbing the coil in the water...i had to disconnect coil plug and plug in again to get the detector working again so not sure what caused that....any idea's ?????

[kt315]

any idea's ????? -- idea is the shielding has to be NOT LEAKED electrostatically to the soil/ground/water and to your hands/body. check all
out attentionally again - coil, housing, cable. housing coil plug has to be shielded inside. ISOLATION everywhere has to be VERY reliable, anotherway you get a trouble. last words for George anyway, I did notice he likes to dublicate my answers.

[Qiaozhi]

last words for George anyway, I did notice he likes to dublicate my answers.

I thought your post was a general comment concerning the shield connection for either p-channel or n-channel MOSFETs, but daverave was looking for a specific answer related to the Surf-PI. My post was meant as a clarification of your post, not a duplication.

[daverave]

i took my surf pi apart today to try and improve it...i noticed that when the power supply drops to below 9v then the detector is silent and stops working...is that normal for surf pi ??? and if so why cannot the detector function below 9v....i read the input of the 5v regulator can go down to about 6.5v before unregulation...so its pointless really changing the regulator to a low drop out type.

[chemelec]

i took my surf pi apart today to try and improve it...i noticed that when the power supply drops to below 9v then the detector is silent and stops working...is that normal for surf pi ??? and if so why cannot the detector function below 9v....i read the input of the 5v regulator can go down to about 6.5v before unregulation...so its pointless really changing the regulator to a low drop out type.

Actually about 7.4 Volts

[daverave]

i did some tests on my surf pi and when i reduce the power supply down below 9 volts the sample pulse dissapears completely and machine dies...im not sure why this happens...the power supply to the delay chip is correct...could anyone please advise.

[chemelec]

i did some tests on my surf pi and when i reduce the power supply down below 9 volts the sample pulse dissapears completely and machine dies...im not sure why this happens...the power supply to the delay chip is correct...could anyone please advise.

The Surf Pi was Originally Designed for a 12 Volt supply, and not all of the circuit operates at 5 volts. Your 555 and the Mosfet Driver need a reasonable voltage. I suspect below 9 volts is not reasonable.

[kt315]

seems you are a philosopher.
add STEP UP converter this is my advise http://www.ebay.com/itm/DC-DC-Adjust...item5664949d3f
you can use now one cell of Li-Ion 18650 on all day with VERY STABILE +12V.