Electronics > Projects, Designs, and Technical Stuff
Motion detector lamp for my dog, which transistor config is suitable?
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JVR:
Just use a small signal transistor to switch on the MOSFET. Its not like you care about switching times, so use the first transistor for what it is, a current amplifier. This will give you enough grunt to switch the mosfet.
cdev:
A webcam makes a pretty good motion sensor and many of them are IR sensitive or have easily removable filters. Combined with a small cheap SBC with USB cost might be comparable to a PIR and the coverage zone and sensitivity might be much more amenable to fine tuning.
james_s:
An arduino? That's a ridiculous suggestion. Has everyone forgotten how to use small signal transistors? You could use a Darlington if you want a single device with sufficient gain. This should be a trivial project.
Nominal Animal:

--- Quote from: james_s on October 26, 2018, 01:47:45 am ---An arduino? That's a ridiculous suggestion.
--- End quote ---
It's just that having the lamp on while the doggo is moving, may not be sufficient, or comfortable.  A delay of some sort is definitely preferred (in my experience with movement-sensitive lights).  And I wouldn't want the light to go on for every little movement.  So it was more about getting options for solving the underlying problem, rather than a suggestion for how to implement the circuit shown.

Also, I did notice OP does not want to use an Arduino.  An ATTiny85-based DigiSpark or a clone, is a compromise. It's the size of an USB connector, and has only 6 I/O pins, but being reprogrammable via USB (yes, in the Arduino environment) would allow fine-tuning the PIR sensor response to best work for the doggo.  I personally would try to PWM (at the maximum frequency the ATTiny85 can do) the light-up and light-down, so that it is smooth, and not annoying, and does not cause an ultrasonic whine the doggo may dislike.

But, if one has already decided to implement the circuit shown in the first post, and anything microcontrollery is verboten, then yes, the suggestion is ridiculous. Apologies if so.
FBMinis:

--- Quote from: james_s on October 26, 2018, 01:47:45 am ---An arduino? That's a ridiculous suggestion. Has everyone forgotten how to use small signal transistors? You could use a Darlington if you want a single device with sufficient gain. This should be a trivial project.

--- End quote ---

I agree with you, I have several microcontrollers and sensors here, part of the Arduino ecosystem, but my goal as always been to make a low part-count project using common components. I tried to make that clear in my first post but not clear enough. For example, this PIR can be set to remain HIGH for 5 minutes and to re-trigger only after those 5min or during them, no need for a microelectronic for timing.

Thanks to suggestions like yours, of using a transistor to trigger the mosfet or use a darlington pair, I found these circuits which I'm trying to adapt to the components and power source I intend to use:

https://electronics.stackexchange.com/questions/216446/lower-current-through-different-transistors
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