PI never gets old - constant power drive with added bonuses.

[Teleno]

Thanks for the fresh ideas Teleno.

How do you look at this, what if we exclude lm317 constant current source (as badass energy eater) and instead use analog feadback loop to regulate NE555 TX pulse width.
This may help to keep current constant during battery discharge.
But, i see, with lm317 positive voltage raill will be less spiky.

240mW at 12V, 180mW at 9V and that includes the power applied to the pulses.

The thing is I don't want to regulate the pulse width but the energy in the coil. That's why I charge the capacitor to a predetermined voltage and discharge it to a second, lower predet. Voltage. At the same time I provide a smooth analog ground. No spikes would be present on the Vcc line. Only the common mode rejection needs to be high, but most op amps provide that.

The pulse width will vary according to the inductance, which can eventually be used for ferrous discrimination.

This time I'm building the project, it's in an advanced stage. I've written and tested AVR code for ADC and EF acquisition, integrator, period measurement and delay control via a rotary encoder. I expect the PCB to be ready in 1-2 weeks, then it'll be soldering time.

[Vadim18]

Thanks for the fresh ideas Teleno.

How do you look at this, what if we exclude lm317 constant current source (as badass energy eater) and instead use analog feadback loop to regulate NE555 TX pulse width.
This may help to keep current constant during battery discharge.
But, i see, with lm317 positive voltage raill will be less spiky.

[Teleno]

The mcemods2.lib I uploaded lacks the TLC081 model. Edit to add the following lines:

*   DEVICE = TLC081
*
*   Rev. A         TLC081 operational amplifier "macromodel" subcircuit
*             created using Parts release 8.0 on 12/17/99 at 15:28
*             Parts is a MicroSim product.
*
*   Rev. B        22 August 2003 By Neil Albaugh: ADDED HEADER TEXT & EDITED MODEL 
*            FROM TLC081_12V_CMOS.lib
*
* connections: non-inverting input
*              | inverting input
*              | | positive power supply
*              | | | negative power supply
*              | | | | output
*              | | | | |
.subckt TLC081 1 2 3 4 5
*
  c1   11 12 4.2895E-12
  c2    6  7 8.0000E-12
  css  10 99 635.76E-15
  dc    5 53 dy
  de   54  5 dy
  dlp  90 91 dx
  dln  92 90 dx
  dp    4  3 dx
  egnd 99  0 poly(2) (3,0) (4,0) 0 .5 .5
  fb    7 99 poly(5) vb vc ve vlp vln 0 23.969E6 -1E3 1E3 24E6 -24E6
  ga    6  0 11 12 417.20E-6
  gcm   0  6 10 99 499.29E-9
  iss   3 10 dc 130.40E-6
  hlim 90  0 vlim 1K
  j1   11  2 10 jx1
  j2   12  1 10 jx2
  r2    6  9 100.00E3
  rd1   4 11 2.3969E3
  rd2   4 12 2.3969E3
  ro1   8  5 10
  ro2   7 99 10
  rp    3  4 6.0581E3
  rss  10 99 1.5337E6
  vb    9  0 dc 0
  vc    3 53 dc 1.4999
  ve   54  4 dc .85993
  vlim  7  8 dc 0
  vlp  91  0 dc 220
  vln   0 92 dc 220
.model dx D(Is=800.00E-18)
.model dy D(Is=800.00E-18 Rs=1m Cjo=10p)
.model jx1 PJF(Is=5.0000E-15 Beta=1.3348E-3 Vto=-1)
.model jx2 PJF(Is=5.0000E-15 Beta=1.3348E-3 Vto=-1)
.ends
* END MODEL TLC081

[Qiaozhi]

Sorry I misspelled the extension. LM4562.sub should have been "LM4562.lib", it's in the zip file.
To be placed in the lib/sub/ folder

Thanks.

[Teleno]

Hi Teleno,

Unfortunately you've missed out the LM4562.sub from the zip file.

Sorry I misspelled the extension. LM4562.sub should have been "LM4562.lib", it's in the zip file.
To be placed in the lib/sub/ folder

[Qiaozhi]

I'm uploading the LTSpice libraries for NE555tr (transistor level model), TLC081 and LM4562.

Symbols:

TLC081.asy and LM4562.asy go to the lib/sym/Opamps folder
NE555tr.asy goes to the lib/sym/Misc

Models:

mcemods2.lib NE555tr.sub TL081.sub LM4562.sub go to the lib/sub folder.

Once done, modify the schematic as follows: delete the NE555 and replace with the NE555tr from the Misc folder.

PS. The DIS pin of the 555 is an open collector, it can be directly interfaced to an MCU pin configured as input with internal pull-up. It goes LOW when the MOSFET is switched off, so the MCU can start counting the delay to acquire the samples.

Hi Teleno,

Unfortunately you've missed out the LM4562.sub from the zip file.

[Teleno]

I'm uploading the LTSpice libraries for NE555tr (transistor level model), TLC081 and LM4562.

Symbols:

TLC081.asy and LM4562.asy go to the lib/sym/Opamps folder
NE555tr.asy goes to the lib/sym/Misc

Models:

mcemods2.lib NE555tr.sub TL081.sub LM4562.sub go to the lib/sub folder.

Once done, modify the schematic as follows: delete the NE555 and replace with the NE555tr from the Misc folder.

PS. The DIS pin of the 555 is an open collector, it can be directly interfaced to an MCU pin configured as input with internal pull-up. It goes LOW when the MOSFET is switched off, so the MCU can start counting the delay to acquire the samples.

[Teleno]

I also set myself the goal of stabilizing the coil energy regardless of the battery charge level. The easiest way was to use a boost converter. It works very stably and reliably.

http://www.eddy.com.ua/archives/784

The boost converter is a solution for existing designs. My goal is to simplify the total design minimizing the number of (noisy) voltage converters - especially the pesky ICL7660's.

The NE555 is an excellent MOSFET driver and has all the additional elements to control both the coil energy and the analog ground rail with the assistance of an op amp. In discrete designs it reduces the monostable count and no regulators are required, just a voltage reference for the CONT pin that can be a 4.7V zener.
As a front end for an MCU it provides the amplified signal referenced to battery GND and reduces the timing overhead, just add a 5V regulator for the MCU if not using a cheap board like Arduino Pro Mini of Adafruit Trinket that already includes it.

I'm now trying to attach an Attiny85 for signal processing and audio synthesis.

[Hamid]

My condolences...

My condolences on the passing of your wife. It's terrible to hear about your loss and I express my sincere sympathy to you and your family.

[Eddy71]

I also set myself the goal of stabilizing the coil energy regardless of the battery charge level. The easiest way was to use a boost converter. It works very stably and reliably.

http://www.eddy.com.ua/archives/784

[WM6]

I used to post regularly up to about 1.5 years ago, but a serious crisis un my life triggered by the passing away of my wife
after 6 months of horrible illness and becoming the single father of a 9 y.o. has robbed me of 99% of my energy and free time.

Teleno, I really sorry to bitter side of life that happen to you and your family.

Stay strong and healthy. Here in your same-minded community, heavy inner things can go easier.

We all highly appreciate your creative and knowledgeable contribution here.

[6666]

Hi Teleno, sorry for the loss of your wife, a difficult time.

[Qiaozhi]

Thank you George.
Try reloading the page cause I've modified the attachments.

Now I know why the links became "unbroken". Not so strange after all.

[Teleno]

Truly sorry to hear about the passing of your wife. Such a terrible thing to happen.

On a positive note though, welcome back to the forum. I'm sure we have things being discussed here that will help to keep you motivated.
Strangely your attachments are being shown as broken links. However, I can see them if I press Reply With Quote.

Thank you George.
Try reloading the page cause I've modified the attachments.

[Qiaozhi]

After a long while away, greetings to all in this great forum!
I used to post regularly up to about 1.5 years ago, but a serious crisis un my life triggered by the passing away of my wife after 6 months of horrible illness and becoming the single father of a 9 y.o. has robbed me of 99% of my energy and free time.
I've been reading you guys now and then though.

I've been so far mostly theoretical but since I'll be soon going into early retirement I hope to be able to lay back a little and bring some electronics projects to life.

That said let's go back to business.

I want a PI that can drive the coil headed exactly at the same power throughout the battery life. Why? Because a normal PI draws the high tank current peaks directly from the battery, and as the voltage and peak current go down so does detection depth. I want consistent performance at the max till the battery gives up really bad.

So I went into invention mode and I came up with this thingy that charges the coil to exactly the same high current value at a constant pulse rate even when the battery is so weak that it can barely deliver 100 mA. The peak coil current and pulse rate are not affected by the battery voltage or its discharge capacity. As a bonus, a wide range of battery voltages can be used.

The basic idea is to have a constant current source I charge a large capacitor C. When the cap voltage reaches a given level VH the cap charges the coil, when it falls to a second level VL the MOSFET fires the coil. The voltage at the cap grows at a constant rate (linear ramp) the drops faster during the coil transient, but only a small step about 0.5 V.

The cap transfers a constant energy value (VH - VL) x C ^2 to the tank.

The pulse rate is constant and determined by I, C, the discharge transient time Tdis time and the reference levels VH and VL: PR = I / ( (VH - VL) x C ) + 1 / Tdis.

Traditional PIs usually require additional voltage converters to create voltage rails above and below the battery voltage in order to feed the analog circuits (see the +5V and -5V in MPP for example.) This thingy does away with that because it uses the cap voltage as the analog ground. We then have three steady voltage levels: battery+ with no glitches because it's feeding a constant current, battery GND and a relatively slow moving capacitor voltage slowly ramping up and down about half a volt around the middle of the battery voltage. Power source noise is dealt with by eliminating rather than adding components!

The analog circuits, e.g. Op Amps have their power terminals connected to battery+ and GND, with the virtual ground being provided by the cap. This means a changing common mode for the analog signals (VH - VL) at about 1 kHz, but modern Op Amps having a CMRR (common mode rejection ratio) well over 100 dB, the common mode noise will be far below the signal noise.

Those of you who've lived long enough will surely recognize the old Wireless World style...

Hell I want to build this **** but some of you may take the lead.

Truly sorry to hear about the passing of your wife. Such a terrible thing to happen.

On a positive note though, welcome back to the forum. I'm sure we have things being discussed here that will help to keep you motivated.
Strangely your attachments were being shown as broken links. However, I could see them if I pressed Reply With Quote.

Update: Now (after posting this reply) the links in your post have become "unbroken". Very odd.