Originally Posted by wsemajb

I realize this isn't straighforward, but how bad is it? How can I wire a 3.5 digit LED display into a circuit designed for an LCD.

I will assume that you have a good reason for doing such a thing.

The two are very different.

If you know which controller the LCD uses you could run the LCD input into a uC and have the uC drive the seven segment display.

It's more of a general question. I looked, last year, for a simple LED thermometer to use in a project. Turns out they don't exist... for less than a hundred dollars. I finally just ordered a used LED automotive gauge off of ebay for prototyping which worked fine, but it gets me no closer to getting something I could order in quantity should I ever decide to market a machine with temperature display.

There are many plans online for LED thermometers. They all require programming code of which I'm ignorant. They would require a tall learning curve, gathering parts, asking permission for code and possible property rights for production, farming out circuit board manufacture and assembly, etc, etc.

Please resist the temptation to flame me for admitting such ignorance on an electronics board. I'm not highly trained in this. I probably make more trouble for myself in the longrun by trying to ferret out those building blocks that I can work with via the internet, but I find it very enjoyable.

I just saw a link for a Chinese manufacture of 3.5 digit red led panel displays thermometers for 4.50 USD in quantities of 100. No mention of whether sender is included or guarantee that it is even LED and not backlit LCD (it's hard to tell in a photo). From there, the prices begin again at around 100 dollars for anything here in the US.

But the point is, I know these panels can be manufactured for less than 10USD each. Considerably less in fact. Noone seems to offer a unit that I can get in quantity economically. There are literally hundreds of different LCD thermometers, with probe, out there in various forms for very very cheap. If it were not too difficult to use the circuit involved to power an LED, I might have some options.

I asked at numerous forums last year, if it might not be as simple as plugging an LM34 or LM35 into the following
LED 5V Common Ground Panel Meter (PM-129B)
without having to insert signal conditioning in between. I was never able to get an answer.