Building a Minipulse Plus Rev D

[ODM]

The CMOS version has a generic complementary output that swings pretty close to either rail, can't source much, and starts dropping off relatively smoothly. The bipolar one has a higher current output capacity, but its output swing is more asymmetric, and there's around 1.5V voltage drop in logic high output. This together with the series diode make for the slower risetime on the timing capacitor to 2/3 supply voltage, despite the bipolar having more current sourcing capability at lower output voltage. I'd imagine that's why the "weaker" cmos output gives a faster rise time.

Off the note, the CMOS version together with a plain resistor to output makes for a quite nice 50% square wave generator.

[Qiaozhi]

"...LT1054 has been synchronized to the TX oscillator, allowing the sampling integrators to eliminate any switching that is introduced into the receive chain."

Can QiaoZhi elaborate on this?

On the scope the period of the LT1054 is shorter than the Tx period. During the Tx period the LT1054 goes high at the rising edge, then low before Tx is done and remains low for about 30us after Tx is done, then back to the original pattern for the rest of the millisecond.

What's the effect of this?

This is exactly the same situation as with the Baracuda design. The voltage converter runs on its own internal oscillator, but can also be run from an external source. However, the TX oscillator has a much lower frequency, and it's just too low to drive the LT1054 (or 7660S) properly. The arrangement in the MPP and the Baracuda cause the internal oscillator to pause, and then re-sync with the TX. This keeps the switching noise synchronized with the TX. If you simply let the LT1054 run asynchronously, you will see what is basically external noise injected into the RX chain.

[Qiaozhi]

QiaoZhi: I believe the inconsistency between TLC555 and NE555 is due to the "unorthodox" connection of the astable, using OUT instead of DISC to charge/discharge the cap. OUT has trouble sourcing current in CMOS (10mA max.)

Yes, that appears to be the case. This "unorthodox" configuration of the 555 is something created by Eric Foster. I think it's intended to maintain a more or less constant TX power with variations in battery voltage. If you raise and lower the power supply voltage, you will note that the TX pulse width varies slightly.

[EasyX]

Intresting what you guys dicuss here in my Thread I dont understand much since i am quite new to all this stuff.

I am thinking about building 1 or 2 coils with the 3DSS pattern from the Chance PI coil thread. I brought up 3 questions there, maybe if someone can answer them. I just have limited time to actually build the coils, since i have access to some more tools right now, but i will be back on the road soon.

Anyway i made progress today to attach switch, Potis and Line In on a plastic box. This box got attached to a 5 AU$ broom Looks funny, but it does the job! I will post pictures when i am finished. It will look really selfmade haha

[Teleno]

I'm looking into the differental integrator and it seems like a liability rathern than an asset.

Let's say the signal at TP3 (Rx preamp) has a time constant of 58us (duration of the sampling pulse) and starts at 100mV. After 58us it's down 50mV. The average is 75mV. The average current in R24 is 75mV/2K2 = 34uA. This current charges C13 (450nF) to a mere 4mV, which is the output at pin 1 of U8a.

Result: we have attenuated the detection signal by -25 dB. U8b boosts the signal by 6.6 (16 dB), still a net loss of 9dB.

Though tau for this example was longish, attenuation for shorter taus is worse and deteriorates quickly. I believe this part of the circuit needs to be revised.

[green]

I'm looking into the differental integrator and it seems like a liability rathern than an asset.

Let's say the signal at TP3 (Rx preamp) has a time constant of 58us (duration of the sampling pulse) and starts at 100mV. After 58us it's down 50mV. The average is 75mV. The average current in R24 is 75mV/2K2 = 34uA. This current charges C13 (450nF) to a mere 4mV, which is the output at pin 1 of U8a.

Result: we have attenuated the detection signal by -25 dB. U8b boosts the signal by 6.6 (16 dB), still a net loss of 9dB.

Though tau for this example was longish, attenuation for shorter taus is worse and deteriorates quickly. I believe this part of the circuit needs to be revised.

http://www.geotech1.com/forums/showt...781#post195781

I tried to calculate gain and Fc for MPP integrator awhile back, above link. I get a gain of 2.62(R21=10k, R22=56k, R23=6.8k, R25=2.2k) Unlike the other integrators, sampling time doesn't effect gain. Sampling time effects frequency cutoff. Looked at formula for R22. Doesn't make sense. I entered 100000 instead of 10 for desired Fc when I made the chart. Don't remember why. Not sure any of it is correct. I get a different gain than you. How do you calculate gain and Fc?

[6666]

http://www.geotech1.com/forums/showt...781#post195781

I tried to calculate gain and Fc for MPP integrator awhile back, above link. I get a gain of 2.62(R21=10k, R22=56k, R23=6.8k, R25=2.2k) Unlike the other integrators, sampling time doesn't effect gain. Sampling time effects frequency cutoff. Looked at formula for R22. Doesn't make sense. I entered 100000 instead of 10 for desired Fc when I made the chart. Don't remember why. Not sure any of it is correct. I get a different gain than you. How do you calculate gain and Fc?

maybe here
http://www.geotech1.com/forums/showt...ntegrator-gain

And maybe here
http://www.geotech1.com/forums/showt...ositive+sample

[6666]

Double post

[EasyX]

Got it working!

[Davor]

You might wish to replace a broom handle with a crutch, and fix the control box with something a bit more sturdy, say a pipe clamp
http://i01.i.aliimg.com/photo/v0/214...pipe_clamp.jpg
Also make sure things are not banging each other in a box.

[green]

maybe here
http://www.geotech1.com/forums/showt...ntegrator-gain

And maybe here
http://www.geotech1.com/forums/showt...ositive+sample

The MPP integrator is different. I'm not smart enough to figure it out. Trying to learn something.

[eclipse]

What is the best op amp for the integrator, CMOS or JFET type?

Most schematics use TL072, maybe it doesn't offer best performance as it's universal op amp?

Do you think changing to OPA2277 would be an upgrade?

[Davor]

Op amps for integrators must have low input bias current, and perhaps the most important - high speed. Point is that an inverting integrator, or the inverting side of a differential integrator, must be able to cope with input pulse as faithfully as possible, or otherwise you get pulse shape related drift on the output.

[EasyX]

The box is attached quite well I guess. Anyway I don't care much about optics and handling, it must work... ��

[Tim]

Here's my standardised set-up. The box is from Kitstop.com.au.($5)They are made by Futurekit Thailand. The armrest and brackets are all made from PVC sewer pipe heated and shaped with a heat-gun. Coil is sewer pipe as well, pressed into a wooden mold after heating to 180C in the oven. Coil top is stormwater pipe(thinner) glued and clamped with white silicone(for 7 days-to be sure it's dry).Filled with white packaging foam.
Upper shaft is 25mm aluminium from the hardware store($10/m) (700mm) and lower is bamboo veneer broom handle($5)(900mm)-very,very strong.
This is my Baracuda. The LED near the switch is seriesed with a 11.6v diode (a bit high) and stops glowing when battery is low.
The charge controller is along side the battery box ($4-ebay) It can charge 3 or 4 18650s.
Last pic shows simple brackets with wingnuts-a piece of rubber bike tube is glued in one half of shaft bracket to clamp lower shaft.
The MPP will need the next size box,or your choice, but it folds up very compact, and has a 1.5w solar charger. The on-board Li-ion controller means it can be charged from any un-regulated 12V source. The 10v reg in green tape was omitted when I changed the 7660 for a 1054.
This is lighter than it looks-about half the weight of the polio crutches used by me and others, and about the same as my Tracker IV.
I have the MPP RevD board from Silverdog now to build, but this 'cuda performs better than any of the MPP vids I have watched......

I hope this shares some useful build ideas.