HH - audio VCO Option - what about IC7c?

[nick_f]

Hi All,

I built the HH ver C and I have some problems understanding the circuit diagram and explanations for the audio VCO. The switch IC7c pin 9 is connected to emiter of Q5 and the pin 6 is connected to N7. N7 is going to Q10, which is not connected for the VCO option. Pin 6 can't remain unconnected.

"If the VCO option is used, Q10, R49, and R50 are not needed." - I suspect that we actually have to install R50 even for the VCO option. Is that correct?

Regards,
Nicolae

[Carl-NC]

"If the VCO option is used, Q10, R49, and R50 are not needed."

That is an error; R50 is needed. Elsewhere in the article, R50 is specified for the VCO option. Sorry for the confusion.

- Carl

[nick_f]

Thank you Carl for clarification.

Nicolae

[rajesh]

hh

hi Carl-NC you have wrote your article. if you use a large dia meter coil to need modifing R3 and R4.actually i need 100hz frequency and 256 us man puse width same as gary has done 47k 47k . can you provide me correct resister of R3 R4 also R1 R2........

[nick_f]

Hi Rajesh,
I replied to your question here: http://www.geotech1.com/forums/showt...8856#post88856
In order to use a larger coil and to get the frequency and pulse width you want, you have two options: either to increase the resistors R1 and R4, or to increase the value of C8. I consider for your needs it is easier to just replace the cap with a 100nF.

Regards,
Nicolae

[rajesh]

hh

Hi Rajesh,
I replied to your question here: http://www.geotech1.com/forums/showt...8856#post88856
In order to use a larger coil and to get the frequency and pulse width you want, you have two options: either to increase the resistors R1 and R4, or to increase the value of C8. I consider for your needs it is easier to just replace the cap with a 100nF.

Regards,
Nicolae

hi nick i has searched over all market but i don't found this number actually i'm from india can you provide me a resister to conect ic5 pin 3 to ground ......rajesh

[nick_f]

hi nick i has searched over all market but i don't found this number actually i'm from india can you provide me a resister to conect ic5 pin 3 to ground ......rajesh

Rajesh, what number are you talking about? If you are refering to the capacitor I recommended (100nF), that value is the same as 0.1uF (microFarad) and it happens to be the same capacitor as you used for C9, C17, C18, C22 and C23.

About the resistor at pin 3 of IC5 to ground. I verified my board and you are right! I am also using NE555 (which is not CMOS) and the pulse doesn't reach 0V (Ground). I added a 5.1kOhm resistor and now it is OK. So the answer to your question is 5.1kohm.

Regards,
Nicolae

[rajesh]

hh

Rajesh, what number are you talking about? If you are refering to the capacitor I recommended (100nF), that value is the same as 0.1uF (microFarad) and it happens to be the same capacitor as you used for C9, C17, C18, C22 and C23.

About the resistor at pin 3 of IC5 to ground. I verified my board and you are right! I am also using NE555 (which is not CMOS) and the pulse doesn't reach 0V (Ground). I added a 5.1kOhm resistor and now it is OK. So the answer to your question is 5.1kohm.

Regards,
Nicolae

hi nick thank's i shall be use this 5.1 kohm resiter......

[nick_f]

Rajesh,
Based on what you told me about continuous sound coming from the detector, it is possible you have other problems in circuit as well. I would recommend you to build a figure 8 coil for testing. I found that my environment is extremely noisy and I spent a lot of time trying to figure out why I was getting all sort of sounds when no target was present. You can use 15 turns on 50cm diameter. If possible shield that with sticky aluminium foil and connect the foil to the ground at one end only (the ends shouldn't touch - see bbsailor instructions for building coils). Also, the figure 8 should have insulation at the center of figure 8. See the photo of my figure 8 coil on http://www.geotech1.com/forums/showthread.php?t=15363

Next, try to detect some metals (for example a large coin) and let me know what is the maximum distance where your detector can detect it. With figure 8 coil, you must not try to detect at the center of the coil!

Regards,
Nicolae

[rajesh]

hh

Rajesh,
Based on what you told me about continuous sound coming from the detector, it is possible you have other problems in circuit as well. I would recommend you to build a figure 8 coil for testing. I found that my environment is extremely noisy and I spent a lot of time trying to figure out why I was getting all sort of sounds when no target was present. You can use 15 turns on 50cm diameter. If possible shield that with sticky aluminium foil and connect the foil to the ground at one end only (the ends shouldn't touch - see bbsailor instructions for building coils). Also, the figure 8 should have insulation at the center of figure 8. See the photo of my figure 8 coil on http://www.geotech1.com/forums/showthread.php?t=15363

Next, try to detect some metals (for example a large coin) and let me know what is the maximum distance where your detector can detect it. With figure 8 coil, you must not try to detect at the center of the coil!

Regards,
Nicolae

hi nick i have a 4.5 inch aluminium shielded coil 26 aws 35 turn's it work fine. there was a problem of noise with ne555. this has been finish when i conecte a resister ic 5 pin 3 to ground. can you recmond me a resister for ic9 ne555

[nick_f]

hi nick i have a 4.5 inch aluminium shielded coil 26 aws 35 turn's it work fine. there was a problem of noise with ne555. this has been finish when i conecte a resister ic 5 pin 3 to ground. can you recmond me a resister for ic9 ne555

Hi Rajesh,
I am happy you solved the noise problem of your detector.
I checked with the oscilloscope the signal at pin 3 of IC9 and the level was also too low (wasn't reaching 0V, which is the upper limit). I added a 5.6kohm resistor and it has been solved. You could also use 5.1kohm, the value is not critical. I will send a new message about Spice simulation of the VCO circuit. I want to make some changes in it, to get a nicer tone than I have now (the pitch is too high for my taste).

Regards,
Nicolae

[rajesh]

HH

Hi Rajesh,
I am happy you solved the noise problem of your detector.
I checked with the oscilloscope the signal at pin 3 of IC9 and the level was also too low (wasn't reaching 0V, which is the upper limit). I added a 5.6kohm resistor and it has been solved. You could also use 5.1kohm, the value is not critical. I will send a new message about Spice simulation of the VCO circuit. I want to make some changes in it, to get a nicer tone than I have now (the pitch is too high for my taste).

Regards,
Nicolae

HI NICK THANK'S FOR GREAT HELP. i need some image of mono sheilded coil [aluminium foil] where should be end of foil and how to ground this and where will be holl in foil i read article of bb saillor

[rajesh]

HH

hi nick hammerhead artical in vco option schematic displayed vallue of c22 .1 uf and part list displayed c22 .47 uf which in these is corect......

[nick_f]

hi nick hammerhead artical in vco option schematic displayed vallue of c22 .1 uf and part list displayed c22 .47 uf which in these is corect......

Hi Rajesh,
I had a look at the pdf file HHv1p5.pdf and all the references I could find about C22 indicate 0.1 uF. Maybe you misread the capacitor number from the circuit diagram? C22 is located between the collector of Q6 to -5V digital supply (check fig 9, page 6).

Regards,
Nicolae