Create this circuit for me

[Dale Willey]

I need to illuminate a combination of 3 lights based on differential voltage. At the low threshold, a single red lamp illuminates up to some threshold where both a red lamp and yellow lamp illuminate. As the differential voltage increases, the red lamp is extinguishes with just the yellow lamp lit until some threshold where a green lamp illuminates together with the yellow lamp. As the differential voltage continues to increase, the yellow lamp eventually extinguishes leaving just the green lamp lit to whatever limit voltage is applied.

by example
0 to 1 volt differential - red lamp
>1 to 2 volt differential - both a red and yellow lamp lit
>2 to 3 volt differential - just the yellow lamp lit
>3 to 4 volt differential - both a yellow and green lamp lit
>4 volt to 5 volt differential - just the green lamp lit

Any ideas?

 

[MikeMl]

I have such a circuit, but it is on another computer. I will post it tomorrow.
The one I built is a overvoltage (red) , undervoltage(amber), voltage ok(green) using a bi-color LED. It has a ground referenced input, but you could add a diff-amp ahead of it...

Sounds like a job for a quad comparator chip.

 

[4pyros]

Look at the LM3914 chip.
Its made for stuff like that.

 

[Flyback]

I would use a state maching, involving three d types and nand feedback logic, because you have inpus and outpus which kind of golike a sequence

Search "Sequencer, Karnaugh maps" on youtube for good tutorials

 

[kubeek]

Why would you use a digital sequential circuit, when the task is analog and maybe you could call it combinatorial?

 

[Flyback]

I though of doing it with a load of window comparators, but you end up with loads of circuitry, as when one compaator trips, it has to disable the others etc etc.

as you know, the easiest way would be a micro with adc

 

[kubeek]

not really, the way the OP wants it is one window comparator per led and the windows overlap, so you don´t need any logic apart from the six comparators and a bunch of resistors.

Actually just four will be enough, if the red band is changed to anything less than 1 and the green to anything over 4, i.e. removing the 0 and 5v checks.

 

[4pyros]

I though of doing it with a load of window comparators, but you end up with loads of circuitry, as when one compaator trips, it has to disable the others etc etc.

as you know, the easiest way would be a micro with adc

I think a part made for the job would be easier, LM3914 chip.

 

[kubeek]

I don´t think the Lm3914 has the 1V overlap he´s asking for.

 

[4pyros]

I don´t think the Lm3914 has the 1V overlap he´s asking for.

It does if wired that way with a few diodes. Old school. LOL

 

[alec_t]

It does if wired that way with a few diodes.

Diodes alone would result in the current per LED varying by a factor of two, if the diodes routed two outputs of the 3914 to one LED to cover the overlap situation. That might or might not be acceptable. Or did you have a specific circuit in mind to overcome that?

 

[4pyros]

Diodes alone would result in the current per LED varying by a factor of two, if the diodes routed two outputs of the 3914 to one LED to cover the overlap situation. That might or might not be acceptable. Or did you have a specific circuit in mind to overcome that?

Use the diodes as OR gates, and select dot mode. Simple.

 

[alec_t]

Not so simple. That will give the current variation I mentioned. Bear in mind the 3914 outputs are constant-current sinks, not simple switches.

 

[4pyros]

Sorry Alec my bad, I see it now.

 

[Dale Willey]

I think the LM3914 chip would work for my purposes. The 1V overlap isnt so critical. I've been looking at the LM3914 chip and was wondering if it's capable of detecting micro voltages. This project of mine is for an airplane angle of attack sensor where the transducers express differential air pressure in terms of micro volts

 

[Dale Willey]

I think the LM3914 chip would work for my purposes. After looking at the specs for the though it isnt clear to me that the chip is capable in the micro volt range. I'm hoping to use a differential air pressure transducer to display angle of attack information for an airplane using this chip. The pressure transducer that I planned on using however supplies the output in micro volts. Anybody know if the chip can discriminate micro voltages?

 

[4pyros]

You would need to amplify the micro voltage with an op amp.

 

[MikeMl]

I think the LM3914 chip would work for my purposes. After looking at the specs for the though it isnt clear to me that the chip is capable in the micro volt range. I'm hoping to use a differential air pressure transducer to display angle of attack information for an airplane using this chip. The pressure transducer that I planned on using however supplies the output in micro volts. Anybody know if the chip can discriminate micro voltages?

Hi Dale,

In its simplest form, the LM3914 just takes a single input voltage range and compares it to ten equal steps. Each step can light a single LED or the LEDs can light progressively from one end to the other. There is some flexability on setting the starting voltage for the first step and the ending voltage for the last step. Typically, the starting voltage might be 0.5V while the ending voltage might be 9.5V or 0.5V per step; certainly not uV per step.

You would have to amplify the output from your differential pressure sensor using an instrumentation amplifier to get the voltage range to where the LM3914 can deal with it. Some low-pass filtering might be required to make the response useful.

I have an aircraft application where I needed to progressively light 8 LEDs (every five degrees of flap position) but the sender was non-linear, so I couldn't use the LM3914 because it only works with equal voltage steps. Instead, I used 8 comparators where the resistor network between the comparators made non-uniform steps.

You could use just four comparators with some steering diodes to select which LEDs to light up.

 

[audioguru]

The LM3914 will overlap its LEDs if an AC voltage modulates its DC input voltage.
Its datasheet shows that its internal adjustable voltage reference has a minimum voltage of 1.25V and the input offset voltage of the comparators prevents less maximum voltage. But the input signal can easily be amplified to feed it enough signal.

My radio controlled Carbon Cub model airplane has only three positions for its flaps:
1) Up. Normal and fast.
2) Half down. Flying slowly.
3) Fully down. Takeoff like a rocket and land like a parachute.

 

[MikeMl]

Dale, check this out, right here on ETO