Replies to Minipulse Plus

[greylourie]

A few thoughts ... For a revision D (or whatever comes next) I'd like to see PCB placers for:
- a 10k resistor between U8 pin5 and GND - this will allow for using bipolar op amps at this place as well, and does not hurt performance in case of a FET op amp
- 100k resistors in series with Q3 and Q4 gates - I'll fit those "Ikebana style" on a Rev B PCB
- a 47pF capacitor can be added in parallel with R22 to stop propagation of switching glitches back to the feedback network.

I think with a good bipolar op amp that does not produce too much noise, and has a decent common mode range, the input gain could be reduced, the integrator stage gain could be increased to compensate, and the sampling could commence a bit sooner. Choice of well designed bipolar op amps is much wider than in case of FET op amps. There is no problem omitting any of these additions or replacing them with jumpers.

Replacing FETs with a bilateral switch seem a good idea. Eric recommended them as well. Small trouble is that in case of Minipulse it would require ±5V supply in a switching logic to power these properly. I can fix this on a Gb board

He mentions it in the image in first post here : http://www.geotech1.com/forums/showt...354#post171354

Like Qiaozhi says, this brilliant project could possibly spawn future advanced models. Replacing J113's is something I thought of with the GS4. Turns out Orbit was few years ahead, with his "Hibrid". A minipulse plus board, in combination with a +/-5v based logic board, would be a logical progression. Minipulse plus could be used as basis to inspire fast low power CS6-like designs. Or something with a bit more "oomph".

As it stands, it is perfect for novices like me. Looking forward to see the completed build thread once it goes up.

[Davor]

I'll go with ICL7660. It is synchronised via 1k resistor, and no pull-ups to pin 6 as with LT1054. So I'll keep R9, but at 1k, and I omitQ2 and R5, and C3/C5 will get beefed up. It must work.

[Qiaozhi]

I'll go with ICL7660. It is synchronised via 1k resistor, and no pull-ups to pin 6 as with LT1054. So I'll keep R9, but at 1k, and I omitQ2 and R5, and C3/C5 will get beefed up. It must work.

The ICL drops out at 10.5V, and there are issues with the maximum input voltage as well. A better solution (IMHO) would be to use a PIC to generate the TX pulse and sample delays, while at the same time driving the LT1054 with a 25kHz equal mark-space ratio sync pulse.

[Jose]

Hello everyone.
I want to replace the transistors channel field effect "N" on my GS4 homemade, built by 4066.
I have several questions, about feeding the 4066., Ie with (+5 and -5) or (+12 and -12).
Same question for the time base, composed of integrated 45038, (+5 and -5) or (+12 and -12).
E seen different configurations in the forum,
I have a partial outline, made of Dip Trace. I appreciate any help.
Jose

[Davor]

If I understood you correctly, you wish to replace the FETs with 4066 switches in your GS4. Unfortunately it is not possible without corrections to the power supply to 45028, and a level shifter for their signal input.
You could add 100k resistors in series with the FETs' gates that would force them to behave.

@ Qiaozhi, I can only get ICL7660A and it separates from its smoke at 13V. I'll figure it out.

[Altra]

@Davor

If you can find a ICL7662, same chip but 20V tolerant

@Jose

Goldscan 5 uses cd4066's with a capacitor diode level shifter

see post 146, schematic posted by Geo

http://www.geotech1.com/forums/showt...matic&p=162575

[Qiaozhi]

@ Qiaozhi, I can only get ICL7660A and it separates from its smoke at 13V. I'll figure it out.

The problem with the ICL7660A is that it's operating range is up to 12V input, but with an absolute maximum rating of 13.0V. Otherwise, it can be permanently damaged (smoke test). With a new set of 8xAA cells the battery pack can reach 12.88V (which is close), and when used as a voltage inverter it drops out at 10.5V (which is 1.31V per cell). If you opt for rechargeables, then 8 cells will only provide 9.6V. This means you need to use 10 cells, and the battery pack voltage will be a nominal 12V. Unfortunately it's not as simple as that, because rechargeables (immediately after charging) have a much higher voltage that can get above 1.3V per cell, and then ... bang!

This is why I prefer the LT1054, with an operating range up to 15V, and (when used as a voltage inverter) it doesn't drop out until 8.4V (1.05V per cell).
Also, the LT1054 provides much lower voltage losses than the ICL7660A.

[Qiaozhi]

@Davor

If you can find a ICL7662, same chip but 20V tolerant

That could be an alternative, but you would need to measure the drop-out voltage.

[Altra]

That could be an alternative, but you would need to measure the drop-out voltage.

Don't know the drop-out voltage? But I have used the ICL7662 with 7 cell nimh packs without problems. The ICL7660's would fail for me, even when used at 9.6V. That is when I searched out the ICL7662.

[Jose]

Thanks to all
What I try to do is GS4, with some improvements as it has in GS5, with the greatest simplicity.
The idea is to try to use bilateral floodgates of 4066 instead of the J113.
In the scheme of the GS5 published, you can see they use the same time base GS4, but with the addition of 4 diodes and 4 capacitors, 1N4148 100 nf.
I hesitated, for I see in some schemes timebase fed (5 and -5 Volts) such as the Surf PI.
In GS4 and GS5, the time base, are fed (12; -12.. GS4 ) and (-10 and -10 ... GS5).
The floodgates of 4066, are fed into the PI, HH1 and HH2 surf with (5; -5).
Attached is a screenshot of part of the scheme, for better understanding and opinion on the matter.
Thank you.
Jose

[Davor]

This is why I prefer the LT1054, with an operating range up to 15V, and (when used as a voltage inverter) it doesn't drop out until 8.4V (1.05V per cell).
Also, the LT1054 provides much lower voltage losses than the ICL7660A.

After a long while, I realised that the whole function og LT or ICL in sync mode here is a dumb MOSFET complementary pair driver with some silly bells and whistles that are not used at all, and that I can get it all by simply replacing the IC with a pair of mosfets, say 2N7000/BS250. And get the whole thing running at 1/10 price of a chip that refuses to get synced. :duh:

I'll see what it takes in LTspice tomorrow.

[Davor]

What I try to do is GS4, with some improvements as it has in GS5, with the greatest simplicity.

I'm not sure what schematic you attached, but this kind of change is a complicated one, and benefits are marginal. You could do better if you replace TL074 in integrators with a faster low noise op amp with FET input.

Diodes and capacitors in the attached schematic form a sort of level shifter that can be used to control 4066, and only because in GS4 the 45038 are supplied with -12V.

[Jose]

Thanks Davor
On reflection, and when in doubt, I think I will use the J113, or any replacement. This way I'll have an easier PCB and fewer headaches.

[Qiaozhi]

The puzzle of how to synchronize the TX oscillator with the LT1054 is now solved!

The solution is ridiculously simple. I had a brainwave and connected a 100pF capacitor between the collector of Q2 and U2 pin7.
Now it's synchronized. Yippee!

Before you do the modification, connect scope channel 1 to TP1, and channel 2 to U2 pin2. You will see the two signals are asynchronous.
Then fit the 100pF capacitor and you'll discover the two signals are locked together. Simple really.

I tested for any unexpected side effects, such as the +5V supply dropping out at a higher voltage, but could not see any difference. There was also no discernible difference in the detector's sensitivity, but at least everyone can stop mourning the demise of the sync pulse. I will update the latest (REV-C) Build Document tonight, and post the fix in both the REV-B and REV-C threads.

[WM6]

Hi Qiaozhi, can you explain what is purpose of mentioned synchronization?