- Sep 11, 2012
- Sep 11, 2012
I have (what I think is) an old oil lamp that used to be my grandmother's which was converted to electric and it has a flickering flame bulb which I think uses neon. The problem is that the light is so dim that it's essentially useless and only serves as a decoration. I wish to use flickering LEDs to increase the light to a useful level. The lamp is in the hall and I only need it to produce enough light to get between the several rooms in my apartment connected by this hall.
I intend to use these flickering red, orange and yellow 3 mm LEDs which I intend to run at 30 mA. The 3 mm LEDs are presumably preferable to the 5 mm LEDs because they'll dissipate the heat more effectively. I intend to grind and polish the LEDs flat or maybe with a convex cone so the distribute their light better. I will use between 14-30 LEDs and I'm not sure what the best colour mix would be.
2. Power supply
For the supply of power I intend to use something like this variable power supply set to 4.5 V with the LEDs wired in series, possibly with a low value resistor, depending on measurements of the output under a dummy load. Once everything is working, perhaps I can drip superglue onto the turning voltage selector so it never gets changed.
3. PIR sensor
To make the lamp switch on and off automatically I'd like to use a PIR sensor circuit of which there are three available on eBay which may be appropriate:
Adjustable Infrared PIR Motion Sensor Detector Module with Control Circuit Board
Pyroelectric Infrared PIR Motion Sensor Detector Module w. Control Circuit Board
Infrared PIR Motion Sensor Detector Security Module with Control Circuit Boad
All of these operate on between 4.5-20 V.
I think I favour the first one because it says something vague about a "photosensitive setting" and I would like it if the lamp only came on after daylight diminished. Specifically, it says to "use CDS (Defaut: included, not welded)". Google tells me a CdS is a light-sensitive resistor (which contains cadium which is harmful to the enivornment). Presumably they meant soldered instead of welded. Hopefully they can be clear about where exactly I'm meant to solder it (I'll ask now).
I've heard that cheap PIR sensors can be poor in performance. Does anyone know whether a "pyroelectric PIR" is likely to perform better? Or are they all puroelectric? I notice the second sensor has a cover with neat-looking hexagons! Neat though they are, I will probably go for the first for the light-sensitivity.
I think I could use two separate sensors to give a wider arc of movement detection, right? Would I need diodes to stop the logic output of one PIR going into the one which has not been triggered?
Of course I will need some transistor to bridge the gap between the PIR sensor and the LEDs. I'm going to need help selecting one. I already happen to have two but I'm not sure if either are suitable:
IRF5305PBF MOSFETs - but these seem to (if I read the specs right) specify a Vgs of 4 V and I don't think that's possible for me, right? I have no idea what I'm doing but according to my understanding, the gate voltage will be 3.3 V from the first PIR sensor and the source voltage will be 4.5 V so the Vgs will be -1.2 V?? Or will the 3.3 V from the PIR sensor be added on top of the 4.5 V input voltage so the gate voltage will be 7.8 V?
Also, what will the voltage drop be across the MOSFET?
BC337-25 NPN 500mA regular ole transistors - apparently the 'emitter-base voltage' for this is 5 V which is, I guess, even less appropriate?
I could find a different power supply (or set this one higher) if the transistor is going to drop some of my power supply voltage before it gets to the LEDs.
Could someone offer some assistance with this part so I can get this show on the road? The current will be 210-450 mA depending on how many LEDs I include, plus the drain from the motion sensors. Thanks!