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Wednesday, 20 August 2014

Acorn Cellular Trail Camera Testing

Fig 1:  Acorn 5210MG and 6210MG
Cellular Trail |Cameras

I often get asked about how I test trail cameras and in particular the cellular versions so here is a brief overview of my test bench setup.

Figure 2 shows the complete assembly of test card, timer, meters and screen monitor.

The test card enables  a basic evaluation of the camera's lens performance and focusing.

The laptop screen shows a timer and clock, the former of which is used to test the camera's trigger time and also time longer events such as image/video sequences, network transmissions and time lapse functions et.c

The timer is triggered by a manual slider and paddle ( figure 3 ) which also triggers the camera at exactly the same time. The resulting photograph taken by the camera captures the timer and shows how long in tenths of a second, it took the camera to wake up and fire its shutter. This is the camera's trigger

Fig 2:  Complete test bench and monitoring setup
speed as illustrated in figure 4.

The manual switching is interfaced with the laptop via a USB serial port converter and I also use a mouse to stop and clear the clock from behind the camera on test, thus avoiding unwanted triggering during sequences such as repeated trigger speed tests for wider sampling.

The camera under test is powered by a 6V 7Ah SLA battery which is monitored to ensure that its state of charge is within the acceptable operating requirements of the camera.

A current meter is connected in series with the positive supply lead to the test camera and
Fig 3:  Camera on test, paddle, and slider with the slider
activated switch below
continuously monitors the current drawn by the test camera. The current meter is also connected via an optical interface and a USB serial port converter to the computer shown on the left in figure 2. This provides a continuous trace on the screen with a sample rate of approximately 0.3 seconds.

When testing cellular cameras the antenna feeder is teed into the input of a broad spectrum RF meter. This is the Cornet Electrosmog meter seen on the left in figure 5.

There is 3dB attenuation by the T piece and then a 30dB attenuator connecting it to the RF meter input. By virtue of the RF meters calibration the combined 33dB attenuation produces a 00.0dB reading on the
Fig 4a:  5MP test image as saved to the camera's SD card
and showing the camera's trigger speed for this event
meter's screen when the camera's GPRS module is transmitting an output power of 2 watts.

Although the RF meter is a broad spectrum receiver which can detect all signals within its bandwidth, it does not suffer interference because it is inserted into the antenna feeder of a high gain GSM band Yagi. This is tuned to the band, highly directional and when the test setup is at rest the meter shows a noise floor of -65dB.

Please note that all my tests are conducted with a low network signal showing 2 to 3 bars and therefore the camera's RF output is always at maximum. In a high to maximum network signal the camera's output will be correspondingly lower which will improve
Fig 4b:  Compressed VGA image as saved to the MMS
folder on the SD card and then transmitted
at the event in figure 4a
battery performance over time.

In addition to the power level reading the RF meter also provides a histogram, bar graph and an LED readout which shows red at the three highest levels. This is very useful when timing the component parts of a transmission event.

The combination of current graphs and RF output monitoring provides a convenient and reasonably accurate method for assessing the cameras condition and performance, with the current graph providing a useful visual signature of a camera's behaviour and state.

Figure 6 shows a typical current graph produced by a test 6210MG set to take a single image and then
Fig 5:  RF meter left and current meter right
transmit an image to an email address via SMTP.

I can't claim this as being laboratory grade accuracy but as an economy solution for efficiently conducting a number of function tests simultaneously it works very well.

This post will also help readers to understand how I gather the information I will be showing in future test results.

My next post will be an analysis of the SMS remote control function.
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This web site is about the wildlife, particularly the mammals, of the Glen Affric National Nature Reserve area in the north west Highlands of Scotland, UK; and the equipment I use to search for them, which is chiefly trail cameras.

I provide a technical support and parts service for the Ltl Acorn range of cameras and the income from this provides for the upkeep of this site and the purchase of cameras for my own surveying.

I hope you find the site useful and informative; and please contact me if you have any questions that I haven't already covered.