Building the Geotech Barracuda Rev A (from silverdog)

[azigta]

you need an oscilloscope! i think your problem is not the coil, not the dumping. i think is the delay. check values for next resistors to be the same like in schematic: r10,r11,r12, r15,r17,r21. how many cm you get for a coke can? and how many you get for something bigger?

WOW! I think you solved the problem!! Thank you so much! R15 was incorrect, it was a 34ohm resistor instead of a 15k one, I don't know what happened there, can't explain it, I always measure everything before soldering. I guess I didn't do it with this one! Wow... I soldered the correct resistor and without adjusting the delay pots appropiately (Which I don't know how to do at the moment) I get this results, very different from the last ones.

American coins:
1 penny-> 13cm
5 cents-> For some reason It doesn't detect it, I guess it has to do with adjusting the delay properly
quarter-> 17cm

Euro coins:
1cent-> 13cm
10cent-> 10cm (surprised me a bit, since it's bigger that the 1cent one, but also the magnet doesn't almost get it, so I guess it has a really low metallic properties, no idea what this coins are made of really, but 1cm and 5cm ones, the magnet catches them hard, 10cm ones, not at all)
5cm coin-> 16cm

Wow I really think you helped me solve the problem. I can't believe I had a wrong value resistor! such a big facepalm...

Now I need to shield the coil, since I unshielded it when I added more turns, (which now I think It wasn't necessary but I won't mod it anymore, I will just shield it as it is. ) I didn't want to shield it jet because I'm going to shield it with copper tape and I didn't want to buy it if I didn't get some good results first.

Also I need to know how to adjust the delay (both the minimum delay and the 10k pot) and what is its function exactly, I don't quite understand it well.

Thank you very much, this differs greatly from the previous measurings, also the beeping is nicer, I don't know how to describe it, but now it isn't as high pìtched as before and is more consistent. I will do more measurings when I have more coins, like 2€ and 50cent, Now I don't have any.

[ionut_mtb]

I have replaced the mosfet, same results

you need an oscilloscope! i think your problem is not the coil, not the dumping. i think is the delay. check values for next resistors to be the same like in schematic: r10,r11,r12, r15,r17,r21. how many cm you get for a coke can? and how many you get for something bigger?

[jladre]

Make another coil. A decent one.

[azigta]

I have replaced the mosfet, same results

[azigta]

Hi, I've replaced the 40106 and I tested with U.S coins, pretty much the same result.

Dime-> 3cm
5 cents -> 1cm (wow...)
Quarter -> 7-8cm
One cent -> 3-4cm

2€ -> 2cm
50 € cent -> 3cm

Small but strong magnet-> 40cm faint signal, 30cm strong signal

It doesn't matter what I do with the delay or minimum delay, same results, or maybe almost the same, I'm not very good at measuring.

Should I replace the mosfet too?

[ionut_mtb]

The MOSFET will stay in avalanche longer with a lower breakdown voltage, and will slightly increase the minimum sampling time. However, the Baracuda is not designed for early sampling, so the the effect of replacing the MOSFET will be minimal in practice.

You don't need a power pot to determine the best value of damping resistor. I've been using a ordinary pot in the damping resistor tool for a long time without any problems.

thanks for the reply, i've tested with ordinary pot, now max distance for average coin is 30cm (very faint signal), 20cm good signal. now better coil and oscilloscope is the key.

[azigta]

You should get it working first before making modifications.

Of course, I was just thinking if that capacitor is ok because I've read that the mosfet is "only 100v" and that made me think that a 16v capacitor wouldn't be enough xD

[Qiaozhi]

but this can limit the depth of the detector, if the flyback is limited to 100v. i don't remember how big the flyback goes. mine barracuda project have max depth of 20cm for a coin. i'm still waiting to get the power pot to find the best dumping resistor/.

The MOSFET will stay in avalanche longer with a lower breakdown voltage, and will slightly increase the minimum sampling time. However, the Baracuda is not designed for early sampling, so the the effect of replacing the MOSFET will be minimal in practice.

You don't need a power pot to determine the best value of damping resistor. I've been using a ordinary pot in the damping resistor tool for a long time without any problems.

[Qiaozhi]

Should I change it then for a 9640? Also, the 1000uf capacitor that I putted there is 16v, is that ok?

You should get it working first before making modifications.

[ionut_mtb]

but this can limit the depth of the detector, if the flyback is limited to 100v. i don't remember how big the flyback goes. mine barracuda project have max depth of 20cm for a coin. i'm still waiting to get the power pot to find the best dumping resistor/.

[kt315]

The irf9530, is only a 100volt device, I've been meaning to ask Q why he changed it.

and? TIP127 is too 100Volt transistor. on 50us PULSE WIDTH a 100V transistor must work.

[azigta]

Should I change it then for a 9640? Also, the 1000uf capacitor that I putted there is 16v, is that ok?

[Qiaozhi]

The irf9530, is only a 100volt device, I've been meaning to ask Q why he changed it.

Hmmm ... that's a good question.

OK - I've looked at Apberg's Baracuda schematic, and it also shows an IRF9530. That's why I kept it the same.
However, it would be better if this was an IRF9640. I'll let Silverdog know, and he can change it in the next batch.

[azigta]

The irf9530, is only a 100volt device, I've been meaning to ask Q why he changed it.

I don't understand the part were you say " I've been meaning to ask Q why he changed it", I think you said that you tried to understand why he wrote 9640 instead of 9530? maybe he just mistyped, or was thinking on other project mosfet.

edit: Wait, by Q you meant Qiaozhi, you were wondering why he putted a 9530 instead of a 9640 in the schematic ?. In that case if I need another mosfet I can go to the electronics store when I go pick the 74hc14 and change it for other one, if Q thinks another mosfet would be more appropiate I'll change it

[6666]

The irf9530, is only a 100volt device, I've been meaning to ask Q why he changed it.