Home 2018 Forums Crumble Development Proximity and PIR Crumb sensors seem temperamental

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    Just wondered if anyone else had had slightly temperamental behaviours with the PIR and Proximity Crumb sensors?

    I know they are a bit of a tricky sensor to get reliable results from, but even when copying the example code from the PDF Guide from 4tronix (http://4tronix.co.uk/crumble/Crumbs.pdf) they seem to give slightly unpredictable behaviours.

    Any ideas?



    Just for info – I’ll post the advice I got from 4tronix below. Maybe it was just too much Sun… I’ll investigate in a darker environment…

    Response from 4tronix…

    “Proximity crumb. This is a very simple device and should be consistent, in a consistent environment. It sends a constant IR signal and simply activates if it gets a strong enough incident IR light. The problem can be that sunlight (and some office/school lights) can provide enough signal for it to trigger even without a reflection. This is a real problem with a lot of static IR sensors like this. It is best to use these away from direct sunlight/windows and bright lights.

    PIR crumb. The PIR module used on the crumb operates by detecting a change in the incident IR levels. So unlike the proximity crumb, it isn’t the absolute level that triggers it, but the rate of change of the incident brightness. Of course, similar problems can cause it to trigger as it is a fairly simple device in truth. It also has 2 trimmers on it which you may want to adjust. One sets the sensitivity and the other sets the delay time. Different modules will probably have these set to slightly different positions, causing different behaviour. To test them when I’ve built them. I turn them on, walk away 3 or 4 yards/metres, count to 15 while standing still, then walk back to the desk with them on. This has always worked fine for me.”


    Ye -same problem with Proximity Crumb when I tried last term. I think 4Tronix wer egoign to make them a bit less sensitive for future batches. All IR sensors have the same problem but since these are normally sitting up on a desk – they are subject to a lot of ambient light.

    An old trick with these sort of sensors is to get a small black rubber tube and place over sensor so that they become much more directional but I’ve not tried that yet with these ones but that technique has proved effective on robots with IR sensors.

    Re PIR sensors – ALL PIR seem to behave randomly (due to the rate of change of signal principle that they work on)

    They are designed to work at a distance so you have to program them on trust – mount them in position – move well away – then approach and see what happens. They detect lateral movement much more than to and from



    Also, don’t PIR sensors have a bit of ‘settling in ‘ time when they first get power? Where they kinda assess the general situation to set a baseline for future ‘noise’?

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