TDI LOW DELAY

[daverave]

ive been using a low delay of 8 uS on a modified TDI and to be honest ive found it a draw back on the beach on the slightly wet dry sand...the detector picks up very tiny bits of foil and other things which sometimes are hard to see with the eye...so im thinking maybe now its best to set the delay at around 10 uS or upwards as digging these tiny bits of foil are a real pain.

[kt315]

you are more and more learn the physics of the process. by hands at first and after then the mind turns up. thats good.
we say НЕ ДОШЛО ЧЕРЕЗ ГОЛОВУ - ДОЙДЕТ ЧЕРЕЗ РУКИ И НОГИ. first army story for newbie soldier.

[eclipse]

Best test results come from the field not in the lab That's so great about this hobby

[Jim in Idaho]

Dave, how did you get the delay to 8??
Jim

[eclipse]

He's probably having the analog version of the TDI. Good luck setting the SL with lower delay as it's MCU based.

[Jim in Idaho]

Aaahh...I wondered about that. It did arouse my curiosity...thanks!
Jim

[daverave]

my TDI is a modified early analog type...i found to get the delay lower you need to use litz wire and also get the cable capacitance down...i found that on semi wet sand which is not completely saturated i can use 8 uS without any problem...but as i said it means digging very tiny flakes of aluminium and such like which is very annoying...but on clean ground the 8 uS would be a good advantage.

[Jim in Idaho]

my TDI is a modified early analog type...i found to get the delay lower you need to use litz wire and also get the cable capacitance down...i found that on semi wet sand which is not completely saturated i can use 8 uS without any problem...but as i said it means digging very tiny flakes of aluminium and such like which is very annoying...but on clean ground the 8 uS would be a good advantage.

Big advantage prospecting for gold, but I've got the SL version, so I'm stuck with 10. Mine does seem to be especially sensitive, however. I did the dweep speed mod, and will soon do the mod that does away with D20, and 21, and also gets rid of C56. Should boost the sensitivity even more. Appreciate the help, Dave.
Jim

[dbanner]

I was always under the impression that anything below say 15us is not usable on the wet sand and certainly not in the water. Based on your observations, this is not the case. Your TDI machine is performing magnificently.
Hope you score some gold, happy hunting.

[daverave]

i have found that the size of the coil is very important where short delays are concerned...if i use my 14" coil on very saturated wet sand then i have to adjust the delay higher to ground balance...but if i use a 12" coil i can use a lower delay...as the smaller coil see's lest wet sand hence lower delay....my wife tried the TDI today on the dry sand using the 8 uS delay and it drove her crazy picking up the tiny pieces of flake foil which are so hard to see...but she did find a very nice palladium mens wedding band ring with the TDI which made her very happy

[dbanner]

That makes my heart feel warm and fuzzy. My wife passed away in 2011. I've been rocking solo ever since.

[Carl-NC]

He's probably having the analog version of the TDI. Good luck setting the SL with lower delay as it's MCU based.

The original TDI used a 555 timer and discrete logic for timing, very easy to change.

The next-rev TDI used an Atmel (later, a PIC) to generate the timing. But oddly the 555 timer was left in the TX path yet it serves only as a buffer. It probably would not be difficult to use it as a pulse stretcher and stretch the TX turn-off time by 2us. Thus reducing the sample time by 2us.

The SL eliminated the 555 so it is purely digital. However, that's all the micro does. If you know how to program a PIC, it would be pretty trivial to replicate what the SL code does and reprogram it with your own settings. A fainl option would be to kludge in a 555 pulse stretcher between the micro and the TX drive.

[Jim in Idaho]

The original TDI used a 555 timer and discrete logic for timing, very easy to change.

The next-rev TDI used an Atmel (later, a PIC) to generate the timing. But oddly the 555 timer was left in the TX path yet it serves only as a buffer. It probably would not be difficult to use it as a pulse stretcher and stretch the TX turn-off time by 2us. Thus reducing the sample time by 2us.

The SL eliminated the 555 so it is purely digital. However, that's all the micro does. If you know how to program a PIC, it would be pretty trivial to replicate what the SL code does and reprogram it with your own settings. A fainl option would be to kludge in a 555 pulse stretcher between the micro and the TX drive.

Interesting, Carl. Sounds like a project for a cold winter's night...thanks!
Jim

[daverave]

Hi dbanner

Sorry to hear that you lost your wife....i know whats its like loosing people you love...i think its something we never get over but somehow live with each day...im fortunate that i have a wonderful philipino wife who looks after me and loves metal detecting and she is far better than me at finding coins and rings...i was a mummies boy for 52 years and only got married at the age of 52 after my mother passed away...im now sixty years old with two lovely children which i never dreamed i would have.....my wife and kids are what keeps me living each day.

[Orbit]

Versions TDI before TDI SL deeper ? I would say based on the view schemes TDI pro and TDI -SL that it is deeper TDI course -sl is quieter .
Otherwise I was writing my hex code for TDI-SL starting at 5us up to 30 us ...