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PostPosted: 24.05.2011 00:08 
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Junior Modder
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Joined: 23.05.2011 23:56
Posts: 2
I'm having a little problem, the signal I'm getting from an IC is HI-Z, High (5V) or Low (0V).

The point being that a led needs to light when the signal is 5V and a different led when the signal is 0V.

I made a circuit that works when the signal is only 5V or 0V.
Image

With that circuit the problem is that when STATUS output goes HI-Z, the current that comes through the first led goes through the base of the transistor and both leds glow dimly.

This shouldn't be a hard challenge, but I've have a hard week at work and my brain isn't clearly functioning as it should.

Would appreciate the help!

----

Eli tulee piiristä signaali mikä on joko: Hi-Z, 5V tai 0V ja pitäisi saada jompikumpi ledeistä syttymään sen perusteella, että onko signaali 5V vai 0V.
Ongelmaksi muodostuu se, että kun signaali muuttuu Hi-Z, niin molemmat ledit palavat himmeästi.
Nyt ei oikein jaksa leikata kaalissa ja en vaan keksinyt tähän mitään järkevää ratkaisua, niinpä päätin tulla tänne kyselemään vähän apua.

Jos joku keksii jonkun helpon jutun millä tämän sais pelittämään, niin arvostaisin palautetta :)


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PostPosted: 24.05.2011 21:16 
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Site Admin
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Joined: 24.01.2002 10:09
Posts: 4683
Location: Finland
Moi.

Hmm... if I understand you correctly, what you need is a logic probe. There are tons of different kinds of circuit available on this topic and you need to go through them to see what offer the particular led action you want. Here are some that I believe that could do the trick:

http://www.neufeld.newton.ks.us/electronics/?p=31
http://www.allaboutcircuits.com/workshe ... ignal.html (scroll to question 6, I would go with this one as it is adjustable...)
http://www.extremecircuits.net/2010/05/ ... probe.html
http://www.instructables.com/id/Logic-Probe-Kit/

More advanced one:
http://www.eleccircuit.com/simple-logic-probe-by-ne556/

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PostPosted: 26.05.2011 22:20 
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Junior Modder
Junior Modder

Joined: 23.05.2011 23:56
Posts: 2
Ahh, those weren't the things I was actually looking for, but the principle of operation is very close to it so I'll modify it just a bit, but I'll certainly use the comparators :)

I actually need this for a LiOn Charger Circuit, the charger IC outputs
0V to the STATUS line when it is charging the battery,
5V when it's done
and switches to Hi-Z if not operating.

This is what I came up with for the led circuitry:
Image

Thanks for the help!

Edit:
Hmm, I tested the circuit in a LM339 on a breadboard and noticed that still one of the lids lit up if the wire is connected to nothing, so I used two 330k resistors to connect the STATUS line (or the probe point, whatever you prefer) to VCC and GND so now it works.
Just wondering if I need to use the same thing on the circuit above?
Because on the breadboard the line was just floating around freely, but the IC outputs Hi-Z, so is it the same thing?


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