Step 7

[Rinkerdink]

Hi,

i think i may may have a problem. Although I have a scope of sorts hoki it's a recorder type so you have to set it up and look at the graphs afterwards which is bit crap. I worked through to step 7 and am trying to get 500mV on tp4, I've short pins 2&3 of PL3 as per instructions but the voltage between tp10 and tp4 is bouncing around a bit and there is unpredictable outcomes when adjusting the brass screw. The voltage changes when passing targets close to my coil though so it seems to be semi working. Should I be disconnecting the coil before adjusting the brass screw to get 500mv?

appreciate any assistance

cheers
chris

[homefire]

No . At this point the coil is still in circuit. But You want a no target situation.

STEP 7
Sampling integrator (see Fig. 11):
Fit R18 (220R), R19/R21 (10k), R24/R25 (2k2), R20/R23 (6k, R22 (56k), C12/C13/C14 (470nF),
D8/D9 (1N414, TP4, Q3/Q4 (J113), U8 (TL062)
Monitor TP4 with an oscilloscope or a voltmeter, and confirm the DC voltage level increases when
a target is placed near the coil.
If you did not make the adjustment to R6 (Step 6) using an oscilloscope, then do it now while
monitoring TP4 with a voltmeter. Set the DC voltage level to around 500mV. Make sure you short
pin2 of PL3 to either pin 1 or pin 3 (before adjusting R6) otherwise the voltage will not change.

HF

[Rinkerdink]

Thanks HF, I had another look this morning and placed my coil on a plastic coil box, Li and behold I got a nice steady voltage and was able to adjust R6 to get my steady as a rock 500mV.

thanks

chris

[homefire]