Building the Geotech Barracuda Rev A (from silverdog)

[azigta]

Hi, today I recieved the Geotech Barracuda Rev A from Silverdog. I ordered the pcb and some components since I had most of the components needed for the project.
Andy at silverdog was very kind and sold me some components that weren't available on the store. Very nice experience. All the components arrivet at very good conditions.

Here's a picture of the components I recieved



All nice and shiny.

I was going to start soldering components from step 1 (+5v power supply) But It turns out that the 78L05 that I have it's the big version... facepalm. So I soldered all the sockets and the rest of the components from step 1. When I finish step 1 I will post an image here. I would like the administrator to give me permission to edit this post whenever I want since I would like to include all the building details on the main post, and post questions (there will be questions I guess...) On the comments.

I'll be posting more details today

[Qiaozhi]

I would like the administrator to give me permission to edit this post whenever I want since I would like to include all the building details on the main post, and post questions (there will be questions I guess...) On the comments.

I'll be posting more details today

You are not able to edit any post after a set period. I think this is currently set to 60mins. After that you will have to make a new post.
We do not allow editing of existing posts after the timeout, as it would affect the continuity of the discussion.

[azigta]

Ok, I understand, I was thinking to do it that way but I can post updates in the comments, no problem. Thanks

[azigta]

Update!
Step one completed, picture here:
Step two completed, picture here:

Step three picture here: can't test it because I don't have a high impedance speaker or an oscilloscope, I will try to find a high impedance speaker, but I've read that there are transformers that adapt low impedance to high impedance, does anyone know about this? Maybe I have some transformer that I can use for this, I take lots of transformers from power supplies and chokes or toroids etc. So I maybe I have something compatible but I don't know what to look for. Anyone knows what can I do to adapt 8ohm speaker to some high impedance value so I can test step three? Thanks

By the way, for now, step three is as far as I can go, as I don't have received the copper wire yet, and it is necesary from step 4 on. Until I get a high impedance speaker I don't want to proceed with the build because I want to test each step before proceeding.

[ionut_mtb]

i used an old phone speaker 100ohms or so. i think is working with any headphones.

[azigta]

i used an old phone speaker 100ohms or so. i think is working with any headphones.

Headphones! that's right! I opened some headphones and they are rated 32ohms, it worked! Thanks to you I have tested the step 3, it works, thanks

Step 3 tested and working. Now I have to wait until I make the coil to build and test the step 4

Edit, in step 2 (-5v supply) There's a 2.2Mohm resistor, I didn't have that resistor and I putted a 2.7Mohm one, it worked nice, I got -5.06v. There are also other resistors that don't seem to be standard, and I only have standard values, so I don't have them, and I will be putting other valued resistors that are similar value there, I will post details everytime this happens, and if it doesn't work, then I'll have to buy it, but I think that the difference is so small it will work

[azigta]

Well, I've got a problem... I'm in step 7. In step 6 there's a resistor , R14, a 20k cermet resistor that has to be adjusted using an oscilloscope, but since I don't have one, the pdf says that I have to build step 7 (the sampling integrator) and then adjust R14 measuring pin 1 of U7 and set it to -2.1v. Also short pin2 of pl2 to pin 1 or pin 3 because otherwise the voltage will not change.

Well, I've done that, and the voltage doesn't change at all... Black probe on the battery black wire, red probe on U7 pin 1, and no matter how many turns and which way I turn the cermet resistor, the voltage doesn't change. I've tried both pin 2 with pin 1 and pin 2 with pin 3. Also, I have pin 3 connected to pin 1 because I've read in another thread that has to be done in order to be able to put a potentiometer with 2 cables, that way you don't care which way you connect it.

Could it be the coil? I built the coil and when connecting it it emmits a high pitch continous tone. When doing step 4 (the transmit tx circuit) I had to put a speaker and measure it in AC mode to test if it was really inducing something into the speaker because I couldn't hear any tone trough some headphones. It measured 5mv when close to the coil, 0mv when far from the coil, so that should mean the tx circuit is working, right?

I have taken out the cermet and measured it and it works, so the cermet it's ok.

I don't know what else to do, I need help. Thanks

edit: I think the lf412cn is broken. Look at this measurings

Without the IC on U7 pins voltage:
1-> goes from 1.87v to 2.65v when a big metalic box is far away or very close to it
2-> 1.83v
3-> 0v
4-> -5v
5-> 0v
6-> 0v
7-> 0v
8-> 5v

With the IC on:
1->0v (no matter what I do with the metallic object)
2-> 0v
3->0v
4->-5v
5->0.21v
6->0.33v
7->-3.71
8->+5.12

Also, is it normal that that tone I hear comming out of the coil gets louder when the metallic object is placed close to it? Wow I didn't expect to hear anything. The sound really comes out of the coil. I've made the test Connecting the coil without all the foil and shielding tape, and it does the same sound.

[ionut_mtb]

what value you have at pin 1 of U7 and minus? when you approach metal to coil the voltage increase?

[azigta]

When no Ic is placed on u7, the voltage increases from 1.87 to 2.65 when a metallic object is close to the coil.

What do you mean with "minus" ? I don't understand. I've posted all voltages in an edit some minutes ago, You might have not seen it. Thanks for the reply

[ionut_mtb]

i meant to say negative (minus - ). i don't know what to say, i'm not an expert i suspect also u7 is damaged. check components and u7 direction on the board. i don't think coil have any problem.

[azigta]

I have ordered a LF412, I hope it works... Maybe electrostatic current damaged the IC, never happened in my life, but who knows... I would like to know if those voltages are right. Does someone know if the voltages are ok? I'm a little bit worried, I don't want to put the new IC there and fry it... I think the board without the IC works fine, because when I place something in the coil the voltage on U7 pin 1 rises, but when I insert the IC, no voltage. I guess that inserting the IC causes a short, so maybe inserting a new IC won't cause the short. In fact I think that the first op amp, which has the + and - on pins 2 and 3, and the output in pin 1, is shorted, while the second op amp is at least not completely shorted, because I detect voltages on the inputs and output.

I guess that without more information, I will have to test the new IC and hope it works xD

[azigta]

Well, new chip arrived, I installed it and same problem. So it wasn't the chip. I thought on desoldering the transistors and testing them, and doing that, I destroyed the pads because I couldn't get the transistors off (I guess that's what happens when you don't use flux) I didn't destroy the pcb traces so I will be able to solder female isolated headers and solder them to the trace tomorrow. I will have to buy new transistors and I don't know if my local electronics store has them. In spain it looks like they are not available... I guess I will buy them from silverdog if they don't have it...
I feel very bad... I hope I didn't damage anything else. When I install the female header and the transistors, I will do all the tests, power supply, the speaker tone thing, etc...

Does anyone know any not too expensive good flux available on ebay? (in the european union). Thanks

[kt315]

I destroyed the pads because I couldn't get the transistors off

http://www.ebay.com/itm/Electric-Vac...cAAOSwYIxYBcHC
http://www.ebay.com/itm/Digital-Sold...4AAOSwZVlXwPgw

[Qiaozhi]

Well, new chip arrived, I installed it and same problem. So it wasn't the chip. I thought on desoldering the transistors and testing them, and doing that, I destroyed the pads because I couldn't get the transistors off (I guess that's what happens when you don't use flux) I didn't destroy the pcb traces so I will be able to solder female isolated headers and solder them to the trace tomorrow. I will have to buy new transistors and I don't know if my local electronics store has them. In spain it looks like they are not available... I guess I will buy them from silverdog if they don't have it...
I feel very bad... I hope I didn't damage anything else. When I install the female header and the transistors, I will do all the tests, power supply, the speaker tone thing, etc...

Does anyone know any not too expensive good flux available on ebay? (in the european union). Thanks

You shouldn't have to randomly desolder components for testing, or replace them by guesswork. In this situation you really need to get access to an oscilloscope, and debug the circuit in the proper manner.

[azigta]

I know, I will buy one, but where I live there are no oscilloscopes so I will buy a new one, but for now, I can't buy one. I thought that the transistors were bad because other than the IC and the transistors, the rest of the components are resistors, diodes and capacitors and I thought that it would be very unlikely to have one of those bad, so I thought on giving the transistors a try xD I know that this isn't the way to test a circuit but unfortunately that's all I can do.