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Old 12-25-2012, 05:35 AM
wahoomy wahoomy is offline
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Default pulsing led

I need to build pulsating LED light,between 6 and 12 volt powersource,but pulse frequency MUST go higher with voltage raise,so if its one blink a second with 6 volts ,it should be like 0.5 sec with 9 volt and so on.i was looking for something like that ,just cant find it on market.thnx ahead for any reply.Btw I`m not a pro in electrics so something more simple would appreciate higher .Thanks
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Old 12-25-2012, 06:57 AM
absf absf is online now
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Have not look deep into it but I think it should be possible with some comparators and a VCO like NE566 or 74LS624. But a simple 12F675 with ADC should be able to do it easily. Wait till all the experts are back from X'mas. May be they have simpler solutions.

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Old 12-25-2012, 05:55 PM
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Bernard Bernard is online now
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Might try the VCO section of a CD4046. R1 around 1m, C1 around .1μf, & from bertus, Fmin = 1/ R2 C1; Fmax = 1/ R1C1
Or a 555 with timing R, [ CdS- LED analog photo coupler ], from pin3 to 2&6. Range adjusted with LED current limiting R & LDR series/parallel R.
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Old 12-25-2012, 09:58 PM
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Ron H Ron H is offline
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This circuit works in simulation. Frequency vs voltage was as follows:

6V      .85Hz
7V      2.1Hz
8V      3.5Hz
9V      5.0Hz
10V     6.4hz
11V     7.7Hz
12V     9.0Hz
Select All
The toggle flip-flop on the output is used to maintain 50% duty cycle of the LED, independent of frequency.
The LP2950 is a 5 volt low-dropout regulator, and is available from Jameco and other distributors.
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File Type: png 555 VCO2 sch.png (24.6 KB, 20 views)
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Old 12-26-2012, 06:07 PM
DickCappels DickCappels is offline
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Old 12-26-2012, 08:54 PM
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ErnieM ErnieM is online now
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I'm on the road with no tools but I did something very similar once,customer required a LED replacement for an incandescent bulb to have very similar brightness when runover 10 to 28VDC range.

Needs: 1 PIC12HV615, 1 resistor for voltage regulator (PIC has onboard current shunt regulator), bypass cap, 2 resistors for A2D ranging, and transistor & resistor for switched (PWM) LED driver. Oh, and the LED.

4 R's, 1 C, 1 Q, 1 IC.

And a little firmware too.
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Old 12-26-2012, 09:27 PM
wahoomy wahoomy is offline
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I`m impressed with quick ,nomerous response ! Thank you all.I now realize,Ishould have mentioned at first ,I want to install this on my pc, and conect it to PCU cooling fan,so when PCU is loaded,it goes hotter ,automaticlly voltage on PCU fan rises,and voltage rise should accelerate speed of blinking,wich would make the machine look lifelike.However can not power some complicated circuit from PCU cooling fan source. Was hoping for something simple , like resistor/cap, some zenner diode maybe...Anyway thank you ALL for botherin on my trouble.I`ll just keep looking further...
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