MS20 Power Reduction Success!

Jon5ja

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Hi all.

This evening I received some parts I ordered for an attempt to reduce the idle power consumption of the MS20 PIR detectors.  The picture above shows the current draw of the "stock" unit versus the modification I just finished.  By changing three components, I was able reduce the idle power consumption to less than a fifteenth the original value.

*** EDIT ***
Here's a link to the modification procedure for anyone who doesn't want to read through this entire thread hunting for it:
Low Power Mods

Components changed were:

1.) U1 changed from an HA17324 to a TLC27L4CN   $0.93
2.) Zener diode D4 changed to an LM385Z-2.5NS    $0.72
3.) Resistor R8 changed from 4.7K to 100K             $0.05 ?

I didn't buy the resistor :)

Because the zener D4 needed some minimum current to behave, the original circuit used a 3.3-volt zener with a 4.7K pull-up resistor, providing 500 uA of bias through the zener.  This was on the edge of the lower limit of working current, as indicated by the fact that the working voltage was 2.5 volts.  I attempted to increase R8 with the existing zener, but the regulated voltage immediately fell off to nearly nothing.

Looking around in the catalogs, I found the LM385Z-2.5 micropower zener -- it only needed 20 uA of current to do its thing, so that meant I could reduce R8 to (2.5 V / 0.02 mA) = 125K.  To be just a hair on the safe side, I used 100K for R8 to bias D4 at 25 uA.

According to the datasheets, typical current draw of the TLC27L4CN is 40 uA, so looking at the schematic, the currents added up like this:

40 uA - TLC27L4CN
25 uA - R6
25 uA - R8
10 uA - R9 (measured)
24 uA - R14
------------------------- 124 uA  Expected total idle current

So, as you can see in the picture above, I'm quite pleased with the 110 uA actually measured after these three modifications were done.

You could lose another 20 uA or maybe 30 uA by increasing the values of R6 and R7, and maybe R4, but we're probably already to the point of diminishing returns.

Hope this is helpful.  Now I'm thinking... maybe a 9-volt battery?

Cheers,

Jon
 

davered1

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I give you another week and I will be able to run my sensors off of my good looks!!!

Good job!! that is LOW!!
 

ArkansasElkHunter

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Thats incredable.  You are THE MAN.   Where did you order the components at.  Is it as simple as it sounds.
 

Jon5ja

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I ordered the parts from Digi-Key.  Unfortunately, they have a $5.00 charge for orders under $25, although if you have a handful of cameras you can probably muster up a $25 order anyway.  When I ordered this stuff, I ordered a bucket full of stuff including that mentioned above, plus various opto-couplers and solid state relays for experimentation.  There's a price break at 25 ea. for lots of this stuff so I have ... lots of this stuff :)  Probably only GAntley is close enough to do the "Hey, neighbor, can you spare a TLC27L4CN?" thing.

The only un-simple thing is replacing the op amp.  If you don't have a desoldering iron, it would behoove you to go get one.  Even with Radio Shack's cheapie desoldering iron, it only took a minute or two to remove the factory chip and solder in the new one.

The LM385Z-2.5 zener looks different than the one it's replacing -- it's in a TO-92 package (looks like the transistors already on the board), but it behaves like a zener.  If you're looking at the flat side of the LM385Z-2.5 with the leads down, the left-most lead is not used... I just cut it off.  The middle lead is the cathode (the "pointy" end of the diode) and the remaining outside lead is the anode.  Spread its remaining legs apart and slide them into the holes formerly occupied by D4.

The 100K - for - 4.7K resistor swap isn't too tricky...

Jon
 

Jon5ja

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OK, I said in my first post above that we were "probably already to the point of diminishing returns" ... but I'll let you be the judge.

I (of course) went ahead and replaced R6 and R7 with 470K resistors, and I replaced R4 with a 150K resistor.  Regulation seems perfect (5.002 volts!) and idle current is now 79 uA.  So, 3 more resistors is worth another 31 uA, so maybe it is worth it...

That'd make the difference from the original a 21X improvement :smile-yellow:

Jon
 

passgas55

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Can these mods be incorporated with the mods of the internal timer?Man that MS20 would be hard to beat. Thanks
 

Jon5ja

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Yes, the the low-power mods should work with or without the other stuff.

One thing I did notice just before I went to bed this morning -- sometimes, if there's just barely enough movement to trigger the circuit, it seems the "shutter time" is sometimes reduced.  Once I noticed that it was only about 4 seconds.

I don't know if this is due to the new op amp having less output current (it is basically charging C13 as hard as it can when first triggered, limited only by the output current capability of the op amp), or if maybe this was something that occurred when I dropped the supply voltage from 12V to 6V.  It might even be a combination of the two.  I'll investigate it tonight and see what I can find.

Jon
 

Tinhorn

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Man that's good,

With the internal 2 stage timer and battery efficiency mods, the MS20 shines even more.

Now Jon, get to work on an Adjustable Sensitivity Feature   he he

BTW    .11 ma's with a 9v battery (590 ma battery ampacity) calc's to 7.5 months !

Can't beat that with a stick.......

Tinhorn
 

jayber

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Excellent work Jon.....and thanks for sharing it with us!  You deserve a :toast-yellow:  Now I'm gonna have to get me some of those parts and try it out!
 

Jon5ja

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Hi, Tinhorn.

The gain is determined primarily by the ratio of R13 to R12 -- currently set to a factor of about 300.

You could obviously adjust it either way, but do you think you typically need more gain or less than what's factory supplied?
 

Tinhorn

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The MS20 sensitivity question boils down to 2 or 3 things I think, and reducing the senitivity will help prevent some problems:

1.  Too many "false alarms", especially in the summer daylight hours
            which is why some are using furnace thermostats to turn
            off the camera when the temps are above ~80 degrees

2.  It has a range of 60 or 70' - which is fine in the daytime I guess but most
    animal pix's occur at night and the flash range is 30' or so.  
              (Little Eyeballs in the dark)

3.  Tweetie birds and other small critters setting off the MS20 too much
           also, probably detecting animals behind the brush that the
           camera can't see thru

           These animals are probably not noticed in the pix's, making us
            think it's false alarms

Tinhorn
 

gantley

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gee thanks jon.....sigh....

i just got the inhibit mod documented....  not this.  and i cant just ignore this mod.

you see guys, this is why jon makes me sick some time....  he is just darn good at this stuff and i have trouble understanding how the transister works.  the stories we could tell.
 

Jon5ja

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Thanks Davered, AEH, pg55, Tinhorn, hag, and jayber for the encouragement!

Re: Tinhorn's sensitivity issues...

1.) It should be relatively easy to add a thermistor to the "inhibit" circuit to disable operation above a particular temperature, although I couldn't use 80 degrees as the cutoff here or I'd never take a picture :)  I considered using a thermistor to reduce the gain of U1B, but I don't think the temperature coefficient of most thermistors is going to be "fast" enough (most change like 4% per degree C) to set the gain without using a bridge circuit, and that would likely require another op amp to implement.

2.) It appears feasible to use the supplied LDR (R22) to modify the gain of U1B for day versus night operation.  Care to guess at objective gain numbers for day and night operation? (Factory gain is about 300)

3.) Yep, generally reducing the gain is probably the answer for this one.

In general, if you just want to experiment manually with the gain, stick a 50K 10-turn pot (so it won't be so touchy) in place of R12 and tweak away.
 

Archilochus

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Great job Jon!!
Good to hear the 27L4 worked out - it's just the part I had my eye on (it's the part I use in most of my "home-brew" sensors).  Replacing that power hogging Zener was pure genius!  Have to check out those parts.

Thanks,
Archilochus
 

coyotebandit

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Jon5ja,

Pretty amazing work, I'm very impressed. I don't suppose you would be interested in looking into the RS PIR to see if any "HomeBrew" improvements can be made? I think sensitivity would be the first thing needed to reduce the number of false pics. I know some commercial units have a switch for animal body size, that might be a nice option. Otherwise a thermostat and day/night operation would be second in my book. Anyway, we all appreciate your hard work and knowledge of electronics. Great job with the MS20 enhancements!

:smiley-thumbs-up:

Thanks

CB
 

gantley

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jon,

with changes in the power input, we will need to make value changes in the inhibit circuit want we?
 

Jon5ja

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Gary:

If you change from 6 volts back to 9 volts, everything should work fine except the shutter time and the inhibit time will be increased somewhat.  That shouldn't be a problem since the shutter time is still much less than the problematic 3-minute zone.

In my case, since I'm using a 5-volt, 30 mA relay, I'd have to add a resistor in series with the coil to get rid of the other 4 volts (4 / 0.030) = 133 ohms, so I'd probably use a 120-ohm resistor in series.  Actually, I just received an assortment of optocouplers (optoisolators?) last night, so I may not end up with a relay in the circuit at all.

CoyoteBandit:

Thanks for the compliment;  if I can come up with one of the RS PIRs I'll take a look at it and see.  I'm about to get tied up at work and at play with other obligations for a few weeks, so I may not get to do much more immediately.

I've already done the calculations for the thermistor mod to shut off the MS20 when it gets hot (a resistor, a thermistor, and a diode), and I also did the calculations for what it'd take to do a daytime or night time only mod (a couple of resistors, the LDR, and a diode), but I haven't had time to decide on a good layout yet for either one, and I wouldn't want to "publish" something I hadn't tested.

Hey Arch:

I just found your old Web page -- I see that you are also using the 81250SGY regulators.  I received some of those yesterday also, and I intended to use one of them instead of the LM385Z-2.5 regulator mod, but I decided it'd be easier to just tell people how to replace those three components than to explain how to get the pin to ground, modify the circuit to still provide the 2.5V reference etc.  You and I have followed a lot of the same thought processes.  Now I'll have to go examine your pages to be sure I'm not coming up with something you already came up with! :smile-yellow:

Cheers,
Jon
 

gtk

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Jon5ja, Tinhorn, Archi  and others who understand this jarble....  

Is there anyway to do a braindump so some of us "not so electronic-literate" people could upload it, and maybe have a clue as to what your talking about when you all are coming up with these "new ideas"  ??  

If it were not for people like ya'll (and jesse), this stuff would never be even remotely possible for me to complete.   Just a quick "thanks"  for making all this fun and understandable (the  understandable part being step by step instructions with pictures) ....

I thinks i'll wait a couple of weeks before building my next cam, so i can incorporate all the latest greatest mods to the ms20....

:smiley-thumbs-up:

Thanks again.....
 

Jon5ja

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Hi, gtk,

Sorry, it's easy for me to get caught up in the moment and start babbling my thoughts.

I've taken pictures of most of the mods I've done, and I'll try to get them posted before long.  GAntley also has been taking pictures and putting them on his Web page, so before long you should have a couple of examples to look at.

I prefer pictures also... instructions are used only as a last resort!

Jon
 

Pgumby68

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An MS20 that could run 7 1/2 months on a 9 volt, now that is what home brew dreams are made of!!!  Like AEH said, You da man. I'm in the same boat as GTK, I need simple drawings and pictures to help me out. I need to know how to make it run on 9 volts first and then how to make it last that long. This is where Tinhorn's brilliance shine through before. The way he dissected the RS-425 made it easy for even the most simple minded of us (ME) to understand. You guys amaze me everytime I log on. Keep up the good work.
 


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