Hi
I have been out of electronic design for 15 years now and therefore I have not kept up to date with current component availability. However the company I now work for requires a very simple circuit that has 2 LEDs on it - green and red. If the input voltage is < a predefined level then the red LED lights, if above then the green one. the circuit needs to be as low cost as possible and very low power.
Any ideas?
Cheers
Ian
Go to the other side of google and enter "comparator" into the search box.
Good Luck! Rich
Yep. One dual comparator and a few resistors. Somebody with that ascii drawing program wanna post it here?
Luhan
"Luhan" a écrit dans le message de news: snipped-for-privacy@j33g2000cwa.googlegroups.com...
Probably not. But with one comparator maybe...
HI
Thanks for the really quick feedback. Not sure if a comparator is neccessarily the right way. The input voltage is also teh supply voltage. Think of this analogy, a guy on a bike has a dynamo attached. As he padals faster the voltage output increases. What I need is that th LED glows if the output is below a certain level (obviously greater than the forward voltage of the LED of course!), but then illuminates the green one above the threshold voltage.
I hope this makes more sense.
Cheers
Ian
At WHAT voltage does the green LED light up?
...Jim Thompson
--- You haven't mentioned anything about the supply voltage, or input voltages, or how low you need the power consumption to be, but here's a general scheme that should work once the resistor values are decided on. The LEDs should be high-efficency devices like HLMP4700's so you can use something cheap like an LM393 for the comparator. View in Courier:
. .Vcc---+-------+--------+---------+ . | | | | . | | [R] | . | | |A | . [R] | [LED] | . | | | | . | +--|---[R]--+ | . | | | | [R] .Vin>-------+-|+\\ | |A . | | >------+ [LED] . +----+-|-/ | | . | | | +---|-\\ | . [R] | | | >--+ . | +--|------------|+/ . | | .GND>--+-------+ .
-- John Fields Professional Circuit Designer
That's still a comparator thing -- split the power supply with a voltage divider, compare it to a reference, light the lights. An LM339 is about as cheap as they come and has enough oomph to drive an LED directly. You can use one side for the 'real' compare and the other just to drive the second LED.
Use an LM324 as a comparator. See page 13 of
On the output, put 1 Led/resistor to + and the other led/resistor to gnd. Use a pot as a voltage divider (outside pins to + and -) and adjust so the the center pin produces Vref.
Ed
John
Thanks for this. The supply will vary from 3v to 12v, with changeover at 9v. It is for a solar application, to give a visual indication of when a threshold voltage has been reached. Also ideally the output voltage should be fixed at 9v once it is reached.
Cheers
Ian
--- You keep shifting the goalposts. First you want a level detector, then you want a power supply threshold detector operating from the same supply which threshold is being detected, and now you want all of the above _plus_ an output voltage regulator for the supply, so we need to know what maximum output current the regulator needs to support, but you haven't supplied that data.
What next?
Why don't you take the surprises out of it and tell us everything you want all at once?
-- John Fields Frustrated Professional Circuit Designer
Ian is only acting like a manager ;-)
...Jim Thompson
Yes, wait for him to tell you that it needs to be zero cost, he needs a thousand of them, and he needs them tomorrow. :)
The idiot is going to come back and say the 74121 did the job for him.
Yabut - if you design the thing for him, you get to change your sig from Frustrated Professional Circuit Designer to Professional Circuit Designer / Mind Reader Extrodinaire
Ed
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