field test unit no 001 "model T"

[Midas]

Hi Moodz, on IC4 4066n are you supplying voltage from the +/- 5volt regs or is it getting supply from the VPP 12 volts ?



Mick

Hi Mick,

From the 4066 datasheet:
Input voltage range, Vis (all inputs) . . . . . . . . . . −0.5 V to VDD + 0.5 V

The positive would have to be +5v since Vin shouldn't exeed VDD by more than .5v with the 4066 (Moodz has already demonstrated getting over 1v of un-amplified signal with some targets). The negative connection would have to be actual ground by the same logic, since if you use the -5v then the Vin would go too far negative during transmit where one side is grounded.

Sorry I know you weren't asking me, but Moodz seems a little busy lately.

Regards
Midas

Edit:
Actually it should be fine to use the -5v, the fets should block the signal from going too low during transmit.

Second edit: ( Mental note, engage brain before keyboard ) It actually looks like the fets may keep the signal below .5v which would possibly would allow you to use the 12v..
You should probably ask Moodz. LoL..

[Vortxrex]

FETs now balanced NP on each input.
NP Mosfet pack used ( 300 volts .... but good for 350 )
4066 works better than other more expensive solutions but use mosfet switch to drive ( like a tc4421 ) Make sure you use the high voltage 4066 ( eg 15 volt rating ).
The THAT amplifier is not the best here ... use opamp DC diff amp.

moodz.

[ATTACH]17470[/ATTACH]

[moodz]

The chip I use is CD4066BCN and the supply rail is set to 17 volts ( 12 + 5 ) and logic ground. In this circuit the analogue ground is the voltage at the "centre tap" of the coil.
The amplifier +/- 5 volt supply is referenced to the analogue ground.

CD4066BCN spec is ....
Wide supply voltage range 3V to 15V
input range is +/- 7.5 volts peak

the spec sheet should really say input is +/- vsupply/2

you can run the chip on more than 15 volts ...this spec is for CMOS logic compliance however we are not using chip for logic but analogue switching

moodz.

[6666]

Looking at the general block diagram of the THAT chip
do you think the lm324 amp would be ok for experimental purposes ?
with a pot for the gain

The only thing I am not sure of is the ref connection which is pin 5 on the THAT

the ref connection seems to equate to the positive input of the last lm324


Moodz has it going to positive, but the lm324 cct has it going to gnd
which should it be for our cct ?

[moodz]

Looking at the general block diagram of the THAT chip
do you think the lm324 amp would be ok for experimental purposes ?
with a pot for the gain

The only thing I am not sure of is the ref connection which is pin 5 on the THAT

the ref connection seems to equate to the positive input of the last lm324


Moodz has it going to positive, but the lm324 cct has it going to gnd
which should it be for our cct ?

Connect the LM324 diff amp equivalent in the same manner. The reason the ref goes to "positive" is because this is the analogue ground ( centre tap of coil ).


moodz.

[6666]

Connect the LM324 diff amp equivalent in the same manner. The reason the ref goes to "positive" is because this is the analogue ground ( centre tap of coil ).


moodz.

Thanks I see the light

( centre tap of coil ).

[Midas]

Opamp instrumentation amp connection

Connect the LM324 diff amp equivalent in the same manner. The reason the ref goes to "positive" is because this is the analogue ground ( centre tap of coil ).


moodz.

I'm still confused. Ref is 12v logically enough but where does the negative supply (+7v in the schematic, pin 4 on the THAT) connect up to ?

[mickstv]

I'm still confused. Ref is 12v logically enough but where does the negative supply (+7v in the schematic, pin 4 on the THAT) connect up to ?

Using your multimeter put the negative black lead on 12 volts then you'll see + and - 5 volts out of the two regulators.



Mick

[Midas]

Using your multimeter put the negative black lead on 12 volts then you'll see + and - 5 volts out of the two regulators.



Mick

I understand the concept of the negative supply, but where does it actually hook into the instrumentation amplifier op-amp arrangement? The THAT 1510 has a reference and a negative supply pin. Op-amps like the LM324 don't..

[mickstv]

The inputs are high ie:- 12 volts, as long as the opamp doesn't have any reference to ground (no resistors or capacitors going to ground) it will see the voltage rails as being +/- 5volts. Thats how I see it anyway.



Mick

[Midas]

Yeah sorry mick, that's not what I meant but it's my fault, I was explaining my confusion poorly. I've got it sorted now, for some reason I had it in my head that the ref connection on the instrumentation amplifier arrangement was the actual gnd pin of the op-amp, pretty much just because it went to ground and the schematic omitted the actual gnd. No consideration was given to the fact that it clearly goes into the non-inverting input... pretty poorly thought out really... I think I'll drink less vodka tonight.

[moodz]

...just my two cents .... a differential amplifier amplifies the difference between two voltages ... ground does not come into it. The difference between the two voltages must only be less than the common mode range and gain of the amplifier. Because the output is single ended the ref connection is the "ground" ... however a true differential amplifier would have a differential output also ( not referenced to ground ).

( actually there is no such thing as ground .... electrons cant read ... they just move in response to magnetic and electric fields )

moodz

[Aziz]

...just my two cents .... a differential amplifier amplifies the difference between two voltages ... ground does not come into it. The difference between the two voltages must only be less than the common mode range and gain of the amplifier. Because the output is single ended the ref connection is the "ground" ... however a true differential amplifier would have a differential output also ( not referenced to ground ).

( actually there is no such thing as ground .... electrons cant read ... they just move in response to magnetic and electric fields )

moodz

You forgot the gravity response force.

Guys, pay attention and don't loose any electrons while you swing the coil...

Shielding may catch them.
You know now, why there is a shielding.

Aziz

[moodz]

Looking at the general block diagram of the THAT chip
do you think the lm324 amp would be ok for experimental purposes ?
with a pot for the gain

The only thing I am not sure of is the ref connection which is pin 5 on the THAT

the ref connection seems to equate to the positive input of the last lm324


Moodz has it going to positive, but the lm324 cct has it going to gnd
which should it be for our cct ?

Redrawn for your viewing pleasure. Note that the GBW of the LM324 is about 1 Mhz whereas the THAT1510 is is very much north of that. The LM324 could be used after a demodulator section. DC accuracy wont be stellar but it will work.

moodz.

[maca404]

This new design is fantastic as a thought exercise how would its power be increased, in this design is the coil energized with 17V ?. Ignoring diminishing returns and battery weight etc is increasing the power as simple as increasing the voltage across the coil ?.