Tweet
Hi all,,It's probably a silly question but can I install Multilayer monolithic capacitors in place of Ceramic capacitors? I'm building the TGSL-Edu pcb that calls for 4 x 100pf, 1 x 15pf and 1 x 10pf ceramic capacitors. I have built the Silverdog TGSL Edu pcb, about 3 years ago, but I have etched this 2nd pcb myself and wanted to know if I can use the monolithic capacitors because I don't have any of the values I need n ceramics. Thanks,,,Marty.
-
-
There is a sub-forum topic for the TGSL here:
https://www.geotech1.com/forums/foru...e-Bandido-TGSL
Better place for TGSL question. Maybe this thread can be moved there.
As to your question:
Best I know is these are the Same or near enough not to matter. Parts I see are listed as MLCC (Multi Layer Ceramic Caps).
https://content.kemet.com/datasheets...03_C0G_SMD.pdf
For the pF values I would only use COG types.
Also sounds like you are going Surface mount. True?? -
Thanks for the reply Watr,,,,I'm not building the SMT Version, it's the original one by Eduardo, the same layout as Silverdog used. I was bored out of my head with this lockdown and had nothing to build now I've just comleted another P.I project. I've been wanting to hone my skills on the O'scope and learn to build and tune up VLF coils so I thought I'd build a fresh VLF Detector from scratch and some new coils for it and just see if I can do it all. I'm ok now with P.I Units and I have bult over 60 working detectors but I'm still finding it difficult to learn how to use my Hantek DSO 5102P properly and I really want to learn and master these VLF coils. I have 2 x IDX'S, 1 X IGSL and 1 x TGSL at the moment but no working coils yet so I'm going t start from scratch with this home etched TGSL and see how far I get,,Lol. What are COG Capacitors? I'm online at the moment trying to order some 'PF' ceramic capacitors but if those COG Caps are better, and are k to install in the TGSL I'll order those. Thanks again waltr,,Regards, Marty.Comment
-
Ok, leaded parts.
COG = NPO and have better temperature coefficients and do not vary capacitance with Voltage across them as much as other caps types (X5R, X7R, etc).
Here are the caps I used:
https://www.digikey.com/products/en?...ds=478-4845-ND
https://www.digikey.com/product-deta...865-ND/4277590
https://www.digikey.com/product-deta...877-ND/4277692
Lots of TGSL project threads in the TGSL sub-forum.
Of course do download the TGSL 101,pdf file to study. It has good scope pictures and good methods to build & tune.Comment
-
Thanks again Waltr,,,,I must've downloaded everything there is on all the DIY detector projects on Geotech over the last 3 years, lol. I love this forum for the amount of knowledge I've learned since joining,,,just wsh I'd got nto the hobby in my teens. I'm ok wth buildng now, still learning about a few components I've never heard of though. I'm just wanting to get more competent with coil 'Tuning' (VLF) really. It's a struggle trying to learn this scope though,,,I can't seem to find anything that teaches you how do the 'Phase' step of the tuning,,,I've looked everywhere,,you tube,,downloaded books,,the manual I have to the scope doesn't tell you much about it. I think if I could find out how to judge the phase part I'll be more successful in tuning coils. I can do all the steps except the Phase. Thanks agan for the info on the Caps,,,I'll order some now as that's all I'm needing to start bulding. Regards, Marty.Comment
-
Is it a Two Channel Scope??
If so then the Scope phase measurement is easy. Connect Scope ch1 to TX oscillator output and Trigger on Ch1.
Connect scope ch2 to RX preamp output.
Now you have a direct comparison of RX verse TX amplitude and phase.Comment
-
Thanks Waltr,,,Yes it's a 2 channel 100mhz scope. When I see the 2 waves how do I measure the phase between them? I think this step is the only one I'm having trouble with. All I've managed up to now is that when I've got the miinimum voltage on the RX and the frequency correct for the TX and RX I've just been moving the coils apart slightly until I can reject ferrite and get the best detection depth. The coils I've been playing with were a little low on inductance (RX 5.7MH and TX 6.02mh) but I placed 21.1nf on one coil and 16.1nf on the other to get the the correct frequencies. The 'D' shaped coils are about 8" diameter when placed together. They were detecting a thin gold ring at about 9", a british 10p at 9-10" and a 1cm diameter foriegn copper type coin at 9". I didn't make an enclosure for these coils or shield them before I started 'practising' to learn to tune so I'm currently making another set that should be the proper inductance this time. I have a better Inductance meter now. It's a DE-5000 but I'm not sure which frequency to measure the coils on as the DE-5000 has 5 different frequencies you can measure at. They are 1khz, 10khz,100khz,100z and 120hz. I know to measure capacitors on the 120 hz setting but unsure with inductance? Each frequency gives me a different inductance so I don't know which one is correct,,lol. I have searched the internet for more information on this but can't find any. Thanks again Waltr,,Regards, Marty.Comment
-
Don't know anything about the L meter but exact inductance is not as important as have the difference of inductance.
For phase on the scope:
First measure the frequency (f) of the TX. 1/f = period.
Now with both TX and RX (RX waveform is same freq as TX) measure the Time between the peak of the TX to the peak of the RX. Divide this by the period and multiple by 360 to get phase shift in degrees.
The TGSL wants about 20 degrees phase shift to obtain proper GB and Disc.Comment
-
Hi Waltr,,,I really do appreciate the help with this,,,,but forgive me for sounding 'Dosy',,I don't think I understand what 'period' is,,Ithough I may know it by another term, if you understand what I mean? Thanks, Marty.Comment
-
The period of an AC wave (sine, square, or other shape) is the time from peak to peak or from zero crossing to zero crossing.
It is also the reciprocal of the frequency.
A little web searching on those terms will give you explanations with pictures.
Since you have coils build the TGSL TX oscillator circuit on a piece of perf board.
This is what I did when starting to play with VLF detector.
Then you can start measuring with your O'scope.Comment
-
Thanks Waltr,,,You really have been a great help. Am I able to measure the RX across the wires like the TX or is better to measure from pin 7 of the pre-amp? I'll have a go tonight with the coil I mentioned earlier,,,it's still set up on the bench. It detects ok but at least I'll be able to see now what the phase is,,,Thanks again Waltr. Regards, Marty.Comment
-
That has been debated at length in TGSL threads.
I prefer measuring the RX signal at the preamp output.
This way the scope does not affect the RX coil and the signal is larger.
As for Air Distance testing, the best ever reported is a 1 Euro coin at 75cm with a 10inch coil.
Most of us get a little less (or don't have a 1 euro coin to test with).Comment
-
Thanks Waltr,,,I'll test across the coil as well as at the preamp output then I can see what the difference is,,I may learn something from it too. I've begun winding some new, more accurate coils as well. Thanks again for the help,,,I'll let you know how it all goes. Regards, Marty.Comment
-
I found this video helpful. Types of capacitors and their specific applications.
https://m.youtube.com/watch?v=J0TjW_0xTJUComment
Comment