Minipulse Rev D first attempt

[Impulse]

ok step 5 at tp3 i used my multi meter and got 11.6vdc and used a can of soup (only thing a had large enough) and the voltage droppped to 11.53vdc seems like all is ok.

[Impulse]

Hey guys i have gone through each step and all have been a success but i have no depth with my test coil which is a 3dss 8" 0.5mm enamelled copper wire coil

step6 i have set the sample delay to 22us


step7 i used my multi meter and i got a large votage swing when i introduce a can to the coil from 500mV to 4vdc

step8 worked as described the SAT worked fine a little slow though

step9 the VCO works fine i am using a 32 ohm speaker (small)

i have tried a new coil also, which is a 10" 0.5mm insulated wire coil 24turns with both of the coils i get about 3" at the most with a usa quarter. any ideas guys?

[Qiaozhi]

Hey guys i have gone through each step and all have been a success but i have no depth with my test coil which is a 3dss 8" 0.5mm enamelled copper wire coil

step6 i have set the sample delay to 22us
[ATTACH]35697[/ATTACH]

step7 i used my multi meter and i got a large votage swing when i introduce a can to the coil from 500mV to 4vdc

step8 worked as described the SAT worked fine a little slow though

step9 the VCO works fine i am using a 32 ohm speaker (small)

i have tried a new coil also, which is a 10" 0.5mm insulated wire coil 24turns with both of the coils i get about 3" at the most with a usa quarter. any ideas guys?

Probe the preamp output on channel 1, and the main sample pulse on channel 2. This will confirm whether you have the main sample pulse set correctly.
Also check you have the optimum value for the damping resistor.

[Impulse]

Probe the preamp output on channel 1, and the main sample pulse on channel 2. This will confirm whether you have the main sample pulse set correctly.
Also check you have the optimum value for the damping resistor.

ok so the preamp output is to the coil? TXRX

if so

and main sample pulse width is 48us

[Qiaozhi]

ok so the preamp output is to the coil? TXRX

if so [ATTACH]35698[/ATTACH]

and main sample pulse width is 48us

[ATTACH]35699[/ATTACH]

Not quite.
The preamp output is at TP3 (U5 pin7). What we need to see is a comparison between the signal at TP3 (CH1) and the main sample pulse at TP6 (CH2).
Both signals need to displayed in the same image. Set the scope to trigger on CH1.

[Impulse]

Hey guys i have taken a trace from tp3 and tp6,

here

i can see that the coil i am using is underdamped (i think please tell me if im wrong) from the 'ringing' before and after the pulse on ch1, i have a spare 100k 22 turn pot i can use to get the coil damped correctly i am going to put it in parallel with R1 how do i know that the coil is 'critically' damped? once the ringing is brought to a minimum? eg use the scope on TP3 and Time/div the same but lower the Vertical voltage so i get a better 'zoomed' view of the 'ringing' eg 500mv.

Am i making sence?

[Impulse]

ok i tried the above and nothing changed i also tried the 100k 22turn in series this also didnt work.

[green]

Hey guys i have taken a trace from tp3 and tp6,

here [ATTACH]35713[/ATTACH]

i can see that the coil i am using is underdamped (i think please tell me if im wrong) from the 'ringing' before and after the pulse on ch1, i have a spare 100k 22 turn pot i can use to get the coil damped correctly i am going to put it in parallel with R1 how do i know that the coil is 'critically' damped? once the ringing is brought to a minimum? eg use the scope on TP3 and Time/div the same but lower the Vertical voltage so i get a better 'zoomed' view of the 'ringing' eg 500mv.

Am i making sence?

My guess. It's not damping. Try changing sample rate to see if you are aliasing on a higher frequency. See if oscillation stays at 70kHz.

[Impulse]

My guess. It's not damping. Try changing sample rate to see if you are aliasing on a higher frequency. See if oscillation stays at 70kHz.

hey green if you are asking me to change the scope frequency then this i cannot do as my pc scope does not allow it.

[green]

hey green if you are asking me to change the scope frequency then this i cannot do as my pc scope does not allow it.

Does the sample rate change if you change the time/div?

[Impulse]

Does the sample rate change if you change the time/div?

yes it does but then most if not all of the sample is off screen, i can try the same test points with different time/div?

[green]

It's oscillating all the time so just change the time/div so you still see the oscillation with a different sample rate and see if the oscillation is still 70kHz.

[Impulse]

Does the sample rate change if you change the time/div?

4mhz

8mhz

[Qiaozhi]

Hey guys i have taken a trace from tp3 and tp6,

here [ATTACH]35713[/ATTACH]

i can see that the coil i am using is underdamped (i think please tell me if im wrong) from the 'ringing' before and after the pulse on ch1, i have a spare 100k 22 turn pot i can use to get the coil damped correctly i am going to put it in parallel with R1 how do i know that the coil is 'critically' damped? once the ringing is brought to a minimum? eg use the scope on TP3 and Time/div the same but lower the Vertical voltage so i get a better 'zoomed' view of the 'ringing' eg 500mv.

Am i making sence?

That's not under damping of the coil. It's external noise pickup. Look at the scope while rotating the coil between vertical and horizontal. You should see the amplitude of the "ringing" change.

[Impulse]

That's not under damping of the coil. It's external noise pickup. Look at the scope while rotating the coil between vertical and horizontal. You should see the amplitude of the "ringing" change.

ok i have tried this and it seems my laptop is the cause! the further the board gets from my laptop the less the erroneous signal presents it self i can only move so far but if get about half a meter away then the signal is nearly gone

so Qiaozhi i take it by "ringing" i am wrong again great! i tried at least!

so for the lack of depth i get my gold ring at about 4"
and a uk £1 at about the same or a little less