Lo all, My first post, and I'm going for gold I'm trying to put together a circuit which will detect temperature and output it in the gradual transition of LEDs So I have three LEDs - Blue, Amber, Red, and a thermistor. When its cold I'd like the blue to be fully on and as it heats up to transition through to full amber and finally full red (Hot). Sounds easy doesn't it? But once I started to think about it I really had difficulty coming up with how three different resistance outputs (low - med - high) could be used to each sink a max current through one of the three LED's sequentially with a proportional hand off of current for a smooth transition? Help Please!! Is it something that just needs a clever resistance network and some transistors maybe? If thats the case then if some1 could confirm it 4 me it would really help me to know I can just focus on playing around with those components. Uber Tnx! Y.
sensor ic Hi, I would not use a thermistor in this case as they are non-linear and since you have one process variable (temperature) and three set- points for the blue led, the amber led and the red led you may find this difiicult to set up with a thermistor. There are precision temperature sensing ic's which work better. The LM34 Precision Fahrenheit Temperature sensor can be used with the LM3914 display driver, should be able to do what you want. The specs on the LM34 are, output 10mv/degree fahrenheit, typical non-linearity of +or- 0.35 deg fahrenheit over a range of -50 to +300 deg, F, accuracy +or-0.4 deg. F.
Nice One! that LM34 seems to be the business. But looking over LM3914's specs, if I read it right it has only two modes on pin9 - dot progression (one led lighting as the previous goes out), or bar (sequentially each LED turning on and staying on). How I could get a continuous transition rather than a discreet jump still illudes me (especially with only 3 LEDs) :S Ok pin 7 controls overall brightness on all pins but the problem remains of tying brightness to the temperature progression such that it sweeps: (Blue max) - (blue and yellow min) - (Yellow max) - (yellow and red min) - (Red max). Even if I tied it to the temperature input on pin5/6 I'd just get a dim to bright transition with Temp increase? Maybe there's an advanced use (mode select) of this chip the datasheets aren't clear on? I do admit I'm a rank novice at understanding all the technical diagrams Tnx. Y.
Won't be perfectly linear, but you could wire the first 3 outputs to the blue led with 3 resistors (sized to give the required milliamps when all are lit, then the next 3 pins wired similarly to the amber led and the next 3 to red. I was going to do something similar for an O2 meter for my car using a single RGB led, but I just haven't gotten around to it yet. (I find a bargraph to blippy for the purpose)
