Modify Motion Sensor Time

Discussion in 'The Projects Forum' started by G-ManX, Jan 14, 2014.

  1. G-ManX

    Thread Starter New Member

    Jan 14, 2014
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    I’m planning on modifying a Westek (AmerTac) Indoor Motion Activated Light (Model# MLC2BC). When activated by motion, the light goes on for a fixed 10 minute duration (no adjustment). However, the most we ever need it on is 2 minutes after an activation. As you can see by the board's layout there does not appear to be any variable components that would allow me to adjust the timer circuitry. Can anyone point me in the right direction as to which component(s) I would need to modify to adjust the timing circuitry down to around 2 minutes? If you look hard you should be able to make out the solder traces through the board. If not, I can take another pic of the other side.

    I used to build 555 timer circuits years ago for fun, so I was hoping when I opened it up I'd see something adjustable like a potentiometer or something variable I could adjust, but no such luck. I am trusting this will be as simple as replacing one of the fixed resistors with maybe something variable. Any advice would be helpful.
     
  2. elec_mech

    Senior Member

    Nov 12, 2008
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    Welcome to AAC.

    Can you post the part numbers on the 16-pin IC and a picture of the back of the board in the same size and resolution as the front?

    I suspect the timing is controlled with a capacitor and a resistor or two like a 555 monostable. If true and we cannot locate the datasheet of the IC, it will probably be easier to find the timing capacitor and change it, although this will not lend itself well to variability on the fly.
     
  3. G-ManX

    Thread Starter New Member

    Jan 14, 2014
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    Thank you for the quick response elec_mech.

    I've uploaded an x-ray (merge) of the board. Also in the lower left corner is a clear picture inset of the IC number.

    I've also added a Chinese data sheet (pdf) and someone's English translation of it (jpg). Interestingly I found both IC data sheets on this site as posted by someone else under an unrelated issue; but now I don't recall who posted them. I would like to have given them credit.

    I hope the new info assists you in assisting me. Thanks in advanced.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Thanks for the schematic. Most of the stuff left of the IC on the schematic looks ot be the differentiator circuit so the IC can detect the small AC signal from the sensor.

    On the right of the IC are two RC timing networks, see C6 and C7. These attach to certain IC pins and should be easy to identify on your PCB.

    I would halve the value of C6 by substituting a smaller cap, then test the operation. Then restore C6 and try again with C7.

    That should tell you if either of these timing caps controls the period that you want to change, I think one will. :)
     
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  5. elec_mech

    Senior Member

    Nov 12, 2008
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    This thread discusses the HS0001 a bit. Most notably is the datasheet eblc1388 posted, attached below.

    You can run it through Google Translate to read it in English. I tried saving the translation, but it will only save it as a webpage and I can't seem to print it as a PDF.

    I don't quite have the time to go through it, but hopefully it will help someone narrow in on the solution. I think pins 3-6 might be where to start looking.
     
  6. G-ManX

    Thread Starter New Member

    Jan 14, 2014
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    So here is the final solution for anyone that may need it in the future. Elec_mech is correct to guide my focus towards pins 3 through 6 on the IC. Specifically I only needed to change the resistance value coming off of pin 3 in order to alter the time the light would stay on.

    The stock value was 180K ohms. I test soldered a resistor in parallel with a value of 10K ohms. This reduced the timer duration from the factory default of 10 minutes down to 30 seconds. The success was awesome, but the time was too short since my goal was to shoot for around 2 minutes. But now I had some solid numbers to work with.

    So the factory resistor was rated at 180000 ohms and ran the timer circuit for 10 minutes (or 600 seconds).

    My test resistor was rated at 10000 ohms and once soldered in, changed the timer circuit to .5 minutes (or 30 seconds).

    So then I decided to calculate to see if the ratio between the 2 resistances matched the ration between the 2 times. As you can see below, they both came out to .05.

    RESISTANCE CALCULATION: 180000 ohm / 10000 ohm = .05
    TIME CALCULATION: 30 sec / 600 sec = .05

    Now that I was able to confirm the ratios were consistent, I could calculate a new resistance that would provide me the 2 minutes (or 120 seconds) I required. By dividing 120 seconds by the factory time of 600 seconds (10 minutes) I arrived at a new ratio of 0.20. I then multiplied the factory resistance value of 180000 ohms by 0.20 and the final answer is a resistance of 36000 ohms which now runs the timer for 2 minute (or 120 seconds):

    TIME CALCULATION: 120 seconds / 600 seconds = 0.20
    RESISTANCE CALCULATION: 180000 x 0.20 = 36000 ohm

    So a 36K resistor gets me the 2 minutes (120 seconds) I was shooting for.

    Thanks to everyone for the support. Elec_mech, the datasheet you uploaded appears the same as the one I offered above (see my post above yours and THE_RB). For future ref, I had also found a jpg that someone created as a loose translation (uploaded in same post above if you ever need it).

    P.S. elec_mech, I had found the same thread you referenced, but didn’t know what to do with it at the time of my first posting, thanks anyway – good find).
     
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  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Or you could have just reduced the calue of C6 as I said earlier. ;)

    Anyway congrats on a success. :)
     
  8. G-ManX

    Thread Starter New Member

    Jan 14, 2014
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    My apologies to THE_RB. I didn’t acknowledge your posts because at first I thought you were off your rocker, and rather than come off as rude, I just ignored you.

    But alas, it bothered me so I persisted in trying to understand how you could possibly think changing the value of C6 could have an affect on the timer portion of this IC when C6 clearly sits on the op-amp side of the chip on my board in the pictures I uploaded (reference my actual pictures of my board).

    Then it dawned on me and I finally realized you weren’t crazy after all – because you weren’t referring to the location of C6 on my real world board from my pictures, but instead you were referencing C6 based on its location in the example schematic I had uploaded.

    I wish to point out that my intent for that schematic was only for IC pin-out reference and the circuit diagram included was arbitrary and had no bearing on the real world conditions I faced on my actual board; and thus the source of my confusion to your response.

    It appears that your C6 in the schematic is my C11 based on the pictures of my actual circuit board (a bit cut off at the very bottom).

    Again I apologize, and acknowledge that you are correct that changing that capacitance value would also be a valid approach to adjusting the timer in this circuit.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    People often think that. At first. ;)

    And no apologies are necessary! :)
     
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