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trigger circuit, only when led blinks

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Jaw174

New Member
hey there, i want to illuminate my printer, just to make it look cool, but i only want the lign to come on then it is printing. how i want to go about doing it, is using this information... when there is movement of the printer heads, or anny activity, the power button blinks indicating activity. normaly it is either normaly on, or off... i want to make a circuit that will trigger the light and turn it on, but only while the light (its an led ) is blinking. it blinks about 2x a seccond. what can i use.. that wont turn the light on unless the led is in flashing mode only, not off and not on. ??
Thanks!
-Jaren
 

Klaus

New Member
Jaren, if it was my printer I would not want to interfere with it to get a trigger signal for your light. How about some lateral thinking approach?
When your printer is idle it draws some small current in standby mode. When it is printing this current must increase to drive the head and feed motors etc.
You can sense this current increase and trigger your light. How? easily enough but you have to be careful since it involves mains power. I did something similar to a fridge to connect a hour meter to check how long it ran.
What I used is one of those glass reed switches, get the longest one you can lay your hands on. You then need to wind a coil into whose centre the reed switch just fits. Current flowing through the coil builds up a magnetic field which in turn closes the reed switch contacts.
Some experimentation is required here to find out just how many turns you need to keep the reed switch open in standby mode and closed when the printer runs. And be CAREFUL here, mains power kills easily and painfully.
You need to measure the current during printing to see what gauge coil wire you need - more current, thicker wire, obviously.
Then you find out how many turns by experimentation. If it takes more than one layer you are better off making a small former to hold the coil compact.
When finished you could fit it into a box with a power cord and a power socket on top. Just plug the printer AC cord into that.
The reed switch contacts are only good for 0.1 amp or so (check this up) so you let it drive a a relay to switch your light. If you get a relay with mains rated coil you don't need an extra power supply for that, the box is then self powered.
You could use that gadget for other trigger applications too as long as the current is in the same range.
Have fun,
Klaus
 

Jaw174

New Member
uhm...thats a great idea... but i was looking more for a "digital" answer.. i feel perfectly at home messing with my printer, as iv had it apart several times before, to change the light color, to add a USB hub in the back (though that just connecto through usb, it still had the printer apart!!) so that i can plug in the printer, then plug in other devices into the back of the printer... now i just want to printer to look nice, but i dont want a big uglu box on the floor, with a wire comming off it and going in.. i want it self contained.. i COULD do that and propaply fit it inside, but id probably use a current sensing coil, and some digital electronics... and make it much smaller... but i want the light to go on, only when the light blinks, so...

Thank for ur thoughts... but i want it digital!
 

k_noe

New Member
Try this circuit. The resistor and capacitor values are not correct. You'll have to select the values so that the period of the RC network will be a bit longer than the blinking period of the printer led.
 

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