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Friday, 19 April 2013

Acorn 6210MG/5210MG Wireless Camera Instability - Continuous Triggering

Fig 1:  A lot of nothing!
There have been a lot of theories floated about recently regarding the problems with Acorn wireless cameras released since last December with the new SIM900 GPRS Module.

The new GPRS module is supposed to have a higher output than the old M10 and although I don't have the means to measure this accurately I'm fairly certain I've worked out what's happening. When the camera is triggered and tries to send an image (doesn't matter if it's MMS or SMTP) the RF output from the wireless module is causing interference with the camera PCB and upsetting its functions. 

Continuous or self triggering:

The amount and type of interference varies from camera to camera.  In particular the interference will cause self triggering in both MMS and SMTP  modes, but as I said before. not in all cameras.

Continuous or self triggering is the most annoying and undesirable of the problems caused by this interference but remove the SIM card and the camera behaves normally.

I had tested several of these cameras and was not getting any self triggering. In fact they were working completely OK sending via SMTP during bench tests and I couldn't understand why so many users were reporting this problem. Then I realised

that more problems were being experienced with cameras with an internal antenna than with cameras using an external antenna and I was bench testing not only with external antenna models but also using a remote antenna.

One particular instance involved a user who had several models set up for commercial deployment and had boxed and loaded them onto a van; but inadvertently had left them switched on with SIM cards installed. These cameras were internal antenna models and whilst being transported, several had fired up on their own. My conclusion is that they had managed to connect in a strong signal area and the resulting internal interference had set off the self triggering. 

Problem workaround:

The camera's wireless module is active for over a minute when attempting to send after each trigger event and it's during this period that it re-triggers; but if you set the delay to over 2 minutes it seems to prevent the camera from rearming until after the GPRS Module has shut down following the previous trigger event.

The current advice from Acorn is to set the cameras delay time to 4 or 5 minutes but as someone said to me this week, this is not a very viable solution when the camera is being used for security as a lot can happen in 5 minutes; and as a high proportion of these wireless cameras are being used in security applications it effectively renders them unfit for purpose.

Some users with this problem have found that when the camera is self triggering like this it will continue until the day/night sensor switches the camera to IR mode, when it will stop retriggering. However once back in daylight mode and once the camera has been triggered again normally, it will again continuously self trigger. This could be a function of power supply voltage and GPRS Module RF output level; and the reason it stops at night is maybe because the LED array is pulling the supply voltage down and thus reducing the RF output. If this is the reason then it's likely that cameras may self trigger less or not at all when the battery voltage is low. 

A possible solution for External Antenna Models:

Fig 2:  Remote GSM Antenna attached to 6210MG
If you're lucky enough to have an external antenna model and if I'm correct with my theory, then you may be able to stop or lessen the retriggering by using a remote GSM antenna connected to the cameras antenna socket by a feeder cable. The vehicle magnetic mount type are easily and cheaply available and would maybe cure the problem.

While I was writing this post Michael in the ROI emailed me to say he had tried as I suggested (see figure 2) and it seemed to have stopped the self triggering, but as it was only for a short test period so far, he was waiting for 24 hours to see if the self triggering recurred.

I will be keeping my fingers crossed and will update this post when I hear from him later.

Long Term Solution:

Obviously the long term solution is for Acorn to redesign the camera to stop the internal interference. I know they are urgently working on this and I am looking forward to news of a permanent cure.

MMS Sending:

There are also problems when trying to send using MMS which may be due to what ports the module will support. There is a firmware upgrade (acorn.cla) available which can be downloaded from my download page which is supposed to correct this but when I tried it didn't make any difference. Other users have reported that after several attempts they got it to load but as I don't use MMS I haven't bothered with it again.

Effect of changing atmospheric conditions:
Fig 3:  Warm front Saturday 06.04.13 early evening.
Out of interest I thought I would mention that whilst testing in a low signal area earlier this month, the test camera had been sending quite happily for several days and then suddenly stopped as if the camera had developed a fault.

It turned out to be our old friend the weather and the camera stopped sending just at the time the warm front shown in figure 3 moved across the north of Scotland.

Remember this if you are working a camera in a marginal signal area and it suddenly stops sending.

I will be particularly interested to hear your comments and experiences regarding the self triggering issue and the results of your attempts to mitigate the problem.

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