Preamp

[Teleno]

FerChrisake, NO INVERTERS please. If I see a 7660 or the like I'll go mad. Synchronous or not they are just pure noise, and not very stable either. Can I suggest a split rail using an op-amp (around 500mA capability) with a truck load of filtering?

What battery do you suggest at what voltage?

If around 9V then a -5V regulator LM79L05 would power the MCU. I reference to the + line because the signal is also refereced to that line.

By the way, OpAmps have about 80dB - 100 dB CMRR (common mode rejection ratio). A 100 mV ripple of a converter will result in 1uV at the output, no big deal.

[Sean_Goddard]

FerChrisake, NO INVERTERS please. If I see a 7660 or the like I'll go mad. Synchronous or not they are just pure noise, and not very stable either. Can I suggest a split rail using an op-amp (around 500mA capability) with a truck load of filtering?

We need supplies so stable they make Cheyenne Mountain look dodgy. I intent to use a programmable load to test the supplies (this included noise injection etc). I think supplies are part of the key to a good PI.

[Sean_Goddard]

Green try sampling JUST BEFORE the Tx pulse instead of 150us after. Just a thought. Also what about a very LONG ground/ efe sample pulse to integrate as much of the noise as possible?

[Teleno]

Did you pick 3 amps peak in reply #165 because that is all you could afford? If not how much can we afford?

Voltage / Resistance, as by law of Nature (Ampere's law).

[green]

As much as you can afford makes sense. The longer the current decays, the stronger the signal of the longer taus.

Let's say you have a 300uH coil with a damping resistor of 700 ohms. The max flyback voltage, say 600V

The minimum current you need Imin is the current barely necessary to reach your 600V, which is: Imin = 600V / 450ohm = 1.33 A

Any current above it (Iadd) will decay linearly trhough avalanche (or snubber).

The formula of the linear decay time is:

I(t) = (Iadd + Imin) - V / L * t;

The linear decay period is approx. T = (0.5 * Imin + Iadd) * L / V;

from this, the additional current Iadd will extend the decay times as follows:

Iadd = 1A; T = 1.16 us
Iadd = 2A; T = 1.33 us
Iadd = 4A; T = 2.33 us
Iadd = 8A; T = 4.33 us

Roughly, for any tau > T the signal increases as a function of the current, 2 x more current = 2 x more signal.

For any tau < T the signal does not increase with the current and it is wasted.

Did you pick 3 amps peak in reply #165 because that is all you could afford? If not how much can we afford?

[Teleno]

This is a larger footprint but looks like it could work.

http://www.digikey.com/product-detail/en/C2M0280120D/C2M0280120D-ND/4935608

Have a good day,
Chet

Good find!

That thing costs almost $40 in my neck of the woods: https://www.conrad.nl/nl/mosfet-cree...omSuggest=true

Mouser.com offers it for $5 : http://nl.mouser.com/Search/ProductD...41-C2M0280120D

Its low ouput capacitance makes a series diode redundant.

[Teleno]

I've been trying to decide what peak current makes sense.

As much as you can afford makes sense. The longer the current decays, the stronger the signal of the longer taus.

Let's say you have a 300uH coil with a damping resistor of 700 ohms. The max flyback voltage, say 600V

The minimum current you need Imin is the current barely necessary to reach your 600V, which is: Imin = 600V / 450ohm = 1.33 A

Any current above it (Iadd) will decay linearly trhough avalanche (or snubber).

The formula of the linear decay time is:

I(t) = (Iadd + Imin) - V / L * t;

The linear decay period is approx. T = (0.5 * Imin + Iadd) * L / V;

from this, the additional current Iadd will extend the decay times as follows:

Iadd = 1A; T = 1.16 us
Iadd = 2A; T = 1.33 us
Iadd = 4A; T = 2.33 us
Iadd = 8A; T = 4.33 us

Roughly, for any tau > T the signal increases as a function of the current, 2 x more current = 2 x more signal.

For any tau < T the signal does not increase with the current and it is wasted.

[Chet]

This is a larger footprint but looks like it could work.

http://www.digikey.com/product-detail/en/C2M0280120D/C2M0280120D-ND/4935608

Have a good day,
Chet

[green]

[Most MOSFETS have low Rds_on to work at this level. The peak current would be (6V - 0.8 (series diode)) / Rcoil. Up to 3 A with a 1.7 ohm coil]

I've been using 1v/battery for NiNH and Alkaline batteries(low usable discharge volts). An IRF740 has resistance of about .5 ohms, need more batteries for 3 amps peak current or lower coil resistance. Some have suggested using 1000 to 1500v fets, higher resistance. I've been trying to decide what peak current makes sense.

[Teleno]

Going back to the preamp, I'm stuck with Eagle at the moment, other CADs won't install in my older Ubuntu and the one that did (ExpressPCB) sucks big time.

Before drawing a plausible schematic I'd like to brainstorm the Power source with you guys (and girls eventually though quite unlikley).

I favor going as low as possible, 5 x 1.2V NiMH = 6V. Eventually 2 x such packs in parallel.

Pros:

- Most MOSFETS have low Rds_on to work at this level. The peak current would be (6V - 0.8 (series diode)) / Rcoil. Up to 3 A with a 1.7 ohm coil.
- Power efficiency. W (power) = V * I. For the same I the power used is lower as the voltage goes lower.
- Weight efficiency. The same Ah (ampere - hour) weight less as the voltage goes lower.
- Lower source resistance. Less batteries in series = smaller series resistance.
- Easy attachment of a MCU control unit.

Cons:

- Longer on-period because the I at the coil rises more slowly. "I(t) = V / L * t"... A 300uH col would reach 3A after 170 us. or 1A after 58 us.
- Voltage converter (doubler) necessary to power the MOSFET gate.
- Voltage converter (negative doubler) to power most OpAmps (single-rail verions are rare, usually slower and more expensive).


What's your take on the power source for an MCU-driven PI?

[Old cart]

Pickit2 just has proven himself. I WAS a member, my posts are on there regarding Proton ICD and Proteus, I can see and prove it. AND I was a VIP I've got the receipts for the payments, in fact I paid for their hosting one month, ALL of it!

Yes, it is mainly a site for hacked software, but the issue is, there are many like myself who would use Mentor for small projects and would love to be able ot teach oursleves so that we can better our job prospects but not all of us have got £40K to spend.

I have a philosophy, If I'm doing it for my hobby, then I'll happily used hacked software, if I'm going to make a project commercial then I will pay for the full version, it's the least the developer deserves. I bought Tsien Boardmaker, cost me £600 then they moved to windows and wanted £1K per year so I dropped them. I now use DIPTRACE and am going to buy the Pro version when I have the cash.

I do not claim to be expert PCB designer but DIPTRACE is a very nice package, has good usability and has a competent fully functional version with 500 pins free to any hobbiest. You just have to send them an email and they will send you a code. See their website for details.

[Sean_Goddard]

Pickit2 just has proven himself. I WAS a member, my posts are on there regarding Proton ICD and Proteus, I can see and prove it. AND I was a VIP I've got the receipts for the payments, in fact I paid for their hosting one month, ALL of it!

Yes, it is mainly a site for hacked software, but the issue is, there are many like myself who would use Mentor for small projects and would love to be able ot teach oursleves so that we can better our job prospects but not all of us have got £40K to spend.

I have a philosophy, If I'm doing it for my hobby, then I'll happily used hacked software, if I'm going to make a project commercial then I will pay for the full version, it's the least the developer deserves. I bought Tsien Boardmaker, cost me £600 then they moved to windows and wanted £1K per year so I dropped them. I now use DIPTRACE and am going to buy the Pro version when I have the cash.

[Qiaozhi]

I think the answer to your question is no. I'm trying to understand what is happening. I've been using a sampling integrator. If I add the GEB sample the no target noise increases. Depending on GEB delay, the GEB sample is 8 to 15 times longer than the target sample which makes integrator gain 8 to 15 times higher during the GEB sample. The noise doesn't increase that much. Looking at the above charts sampling is causing some or a lot of the noise. Is it because noise isn't repeating in the short samples, sample time jitter or something else? Don't know yet.

Could it be because your GB sample has a higher gain than the main sample to compensate for the loss of target signal?
Therefore higher gain equates to more noise. (Using a longer sample pulse is the same as increasing the gain.)

[green]

Hi Green


The charts are a great help. And your chart of the coil sweeping over a nickel explains the 10 Hz response. Your two receiver coil arrangement appears to do a good job of eliminating common mode EMI.


Does the frequency of the target eddy current slope inside of a 10 usec target sample gate need to be considered in later processing?


Thank you,
Chet

I think the answer to your question is no. I'm trying to understand what is happening. I've been using a sampling integrator. If I add the GEB sample the no target noise increases. Depending on GEB delay, the GEB sample is 8 to 15 times longer than the target sample which makes integrator gain 8 to 15 times higher during the GEB sample. The noise doesn't increase that much. Looking at the above charts sampling is causing some or a lot of the noise. Is it because noise isn't repeating in the short samples, sample time jitter or something else? Don't know yet.

[Qiaozhi]

Sean - I have registered a request to join the Sonsivri forum, but it requires someone to actually invite me to join for free. Otherwise it costs $20.
Please can you go to the Invitation Request section of their site and click on "Invite this person"?
Thanks.

I would need the invite for Sonsivri too. Here's my request: http://www.sonsivri.to/forum/index.p...=61849.new#new

Alas it is one forum where the rules are VERY harsh. I havn't been on there for over a year so they booted me even thought I was a paying member.

BE CAREFUL, the admin there are VERY quick to punish for infgringements. DO direct downloads, NO files on the forum, links ONLY. They have all sorts on there, I've even seen Mentor somewhere!

I will try to get back on there, I was Sidley65.

Have just re-applied.

Hmmm ..... Sean is absolutely correct about Sonsivri.
In an attempt to get my post numbers to a level where I could invite both Teleno and Sean (30 posts), I replied to a post there yesterday in the Win10 GUI thread (which is in the General section) where others were comparing Linux to Windows 10. There were a few Linux supporters there, so I added some positive comments. Then today I got a warning about being involved in a pissing contest! And now I'm muted, so cannot even lodge a complaint.
As far as I can see from having read several of the threads there, the site is really only a conduit for illegally exchanging pirated material. The discussions lack any serious technical content, so I wouldn't cry too much if you never get access.

Hahah!
Sean - I also looked at all posts made by pickit2 (the Admin who muted me) and I found this ->
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Quote from: Sidley65 on January 27, 2016, 09:16:44 21:16

Country	UK
Note	Electronics Engineer specialising in, well everything really. Was previously a VIP member but it lapsed (sorry I was involved in other things).

You was not a VIP member: we look after VIP members:

don't forget we have a long memory too.. & system logs too.
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They've got some serious issues on that site. Probably best to avoid.