LSM01 crazy ness

[palmlodge]

A timer is not going to solve this.

 

A timer is fine for when you want to start activating devices at dawn/dusk - bt if you have other logic which checks for the current state of the light sensor, there is a large window where this all fails.

ie if you have door zones that check for light levels to activate exterior lights, these wont work for that period.

Again this HAD been working fine for over 5 years with no timers !

[ident]

I dont see why a timer would not work  if you have other logic which checks for the current state of the light sensor

It is only during the dusk or dawn, ie when the light level is at the theshold setting that the sensor will report either on or off. It will not fail, as the sensor will be either on or off when you check it which is not wrong  as the light level could be either way.

It does not matter at all if the sensor changes state over the course of a few minutes at this time because I assume you only would check the sensor at a specific  time

if you are constantly checking the sensor state to do your logic and you need a consistent state, you can also use a timer in a similar way to set a flag, and just check the flag. If I am not understanding your application perhaps you could supply more information

I dont have any idea why it did not have any transitons for 5 years, as the LSM has not been changed during that time. Perhaps the sensor you use is now more sensitive than before. Our tests here show that we do get this fluctuation

Coments from other users who can shed light would be welcome

[on4cet]

Just trying to help a hand, i thought of the hysteresis which is mentioned in the LSMmanual.  I will put the extract here :

----->

6. Place the light sensor where the ambient light DAYLIGHT
conditions are brighter than the required threshold VR1light level. The LED should be OFF. If not, adjust
VR1 clockwise (CW) until the LED turns on. Note
the position of the trimmer wiper. Now Adjust the
trimmer so that it is between the two positions. The switching point is subject to hysteresis,
i.e. when the LED turns on, the light level has to go some way below the point at which it
turned on, in order to turn off. This is so that at the threshold light level, the output does not
oscillate between on and off.

<-----

  When looking at this, it shouldn\'t oscillate between on & off that much, and thinking of my own installation, can\'t remember seeing the input change ... 

I think there must be something else, because, looking at the text of the lsm manual :

When it goes dark, the LED goes ON, but according to the manual, the light has to be a lot brighter than the switching point at which the led turned ON, in order to put it OFF

Could it be something with the VR1 trimmer ?  Dust in it ?

  Kind regards,
 
Bart

 
PS. I find it strange that the light level changes at 2.4x or 2.5x PM ??  I live in Belgium, which only differs 1 hr with the UK, and at these days, my lsm changes state at about 7.45 AM and 18.15 PM (approx.) Something to investigate ???

[Pgordon]

I had an \"original\" LSM01 which, once I got it adjusted \"just right\" didn\'t seem to oscillate much around the dawn/dusk switching points. I recall the LSM zone switching \"cleanly\" at the changeover point, and doing so within about 20 minutes of the \"official\" sunrise/sunset times for my location. I Was very happy with this performance! Then unfortunately, some local wildlife eat my sensor, and I replaced the LDR and the internal resistor with alternatives from CPC. The internal resistor is a 20K one I believe.

The performance characteristic is now sligtly different.. - I *am* still progressively fine-tuning it though, so I may yet get better results. What I have noticed however, is that I still don\'t have the switching point quite right, and the adjustment of the trimmer is in a different range (presumably this is linked to the value of the resistor?) - previously, the perfect trimmer position was about 25% from the leftmost stop position, This time round I started from that position and have been gradually moving back to the leftmost stop position and observing the result. As stated above, it\'s getting better, but still not spot on, and I need to go a little further back. - Trouble is, I\'m already almost right back to the leftmost stop position on the trimmer, and there\'s not much more adjustment possible in the direction I need to go.. (I have maybe 5% more range to play with - hopefully that will be enough).

I am also noticing that it does seem to oscillate more around the switching point, and will switch on a dull afternoon if a dark cloud goes by for example. I don\'t think it did this as much previously.

My LDR is positioned such that it is not affected by passing car headlights, street lights, and so on. I agree that the hysterisis thing needs a bit of attention. I have not yet tried the zone sensitivty setting recently suggested, so I\'ll implement that very soon. I don\'t have any great objection to using a timer to eliminate the hysterisis around the switching point, but I have a great objection to this arming the system incorrectly due to a bug! - so that\'s not an option until that issue is rectified....

I see Gareth\'s point about the other logic though... - many many other responses may just check the LSM zone status to determine actions, - the LSM zone status may be wrong not only around the dusk/dawn switching points, but also (in my case at least) on a dull day... - Granted this *could* be worked around by expanding the logic (using flags etc), and if starting from scratch this would be sensible to do anyway. However, this may be a real PITA to adjust lots of pre-existing responses to now check a flag rather than the zone status directly...

Of course, if Comfort had a RTC, and could reference the time in responses (and even knew when sunrise/sunset was) might help quite a bit!!! (but that\'s for another thread methinks!)

HTH

Paul G.

[on4cet]

Paul,

 

If the resistor value of the LDR is different, you need to replace the shunted resistor too ... I thought I even had to mount one of 50KOhm ...

If light level goes down, resistance gets higher ... With that in mind, adjust that resistor ...

 

Kind regards,

 

Bart

 

[Pgordon]

Hi Bart,

Whilst I don\'t pretend to actually \"understand\" the relationship between the LDR, the internal resistor, and the trimmer, I was made aware of the need to match the value of the internal resistor to that of the LDR... the 20K value was recommended as the \"right\" match for the particular LDR that I ordered from CPC...

Paul G.

[on4cet]

Hi Paul,

It may seem strange, but I had to mount a 50 K resistor, although my LDR measured about 20K at normal light conditions ...

And I thought I read somewhere that the resistor should be equal to the LDR (at normal light conditions) when talking about the resistance, so, normally I had to put a 20K resistor in, just like you, but couldn\'t get the LED on at dusk, so just went to 50K and all went fine ...

I\'m sure you\'ll work this out Paul !

 

Kind regards,

Bart

 

[ident]

Here is some insight as to the sensor and the resistor that is needed

The resistor value should be roughly matched to the sensor that is used. To do this you should measure the resistance of the sensor ( Light dependent Resistor) at about the time where the threhsold is set (normally dusk or dawn). Hence if the LDR resistance is 50K use the nearest resistor value (47K or 51K)

The effect of the series resistor is important for sensitivity. The larger the value of the reisistance relative to the LDR, the less sensitive the sensor will be, and vice versa

This could be an important factor as users may be using different sensors and resistors supplied by CHC

If the sensor is too sensitive, then small changes in light level will cause large changes in voltage relative to the threshold and the hysteresis. The fixed hysteresis would have little effect

hence a solution to oversensitivity would be too use a larger value of series resistor, which would allow the hysteresis to have a greater effect

This could account for different experiences of users regarding multiple switching around the threshold conditions

Pointing the sensor away from direct light is also important

The LSM manual will be updated to include more guidance

The LDR that we supply can be found in Farnell  part number [img]file:///C:/DOCUME%7E1/LUCHIU%7E1/LOCALS%7E1/Temp/moz-screenshot.jpg[/img]7482280

[palmlodge]

ident
  Thats certainly not the photocell that Comfort Uk are dishing out. This may explain the issues.
  Could you recommend some part numbers for a 20k, 22k, and 50k resistor from farnell ?
  I\'ll order those and give that a go.

[Comfort Home Controls]

Hi Gareth

The LSM01 we sent out to you has the Cytech/Farnell LDR and not the CPC version we have been using as a replacement (which incidentally, works fine for last few years with everyone elses systems).

I had advised you to default the system to prove if the problem was due to the ccl file, how did that go?

Also, the alluminium conversion brackets for G1 to G2 DO NOT cause any bridging of the 0v to the PCB track, they are isolated from the PCB tracking and should not cause a problem.

Andrew Roberts
Comfort Home Controls
www.home-control.co.uk