3 line to 7 line decoder, got a name?

Thermometer code.

will

On a sunny day (Tue, 08 Jun 2010 21:35:41 +1000) it happened Grant wrote in :

EPROM?

Don't think so, going to be a PIC in there anyway as there's a six bit up/down counter plus logic for high/low power switching --> outside the logic there's going to be analog stuff with power opamp or three to perform the fine stuff. This decoder thingy is just so I don't need to switch binary weighted loads beyond a certain size, just turn a bank of seven same sized ones on in sequence instead. Reduce the power glitches during DAC settling time.

Just bugs me that I seem to recall there's a logic chip does that decoder function that leaves the lower lines on, but only chip I can think of is that LED bar graph driver from NS (LM3914). Not because I want to use it, just so I can stop wondering about it.

Grant.

You're not thinking about the reverse function (priority encoder) are you?

Best regards, Spehro Pefhany

will

LM3914?

TICPAL22V10?

If you have enough of a supply voltage, a CD4051 can do it by having the LEDs of the optos in series.

Thank you, that's it, I had to use a priority encoder couple or three months back, it's got a similar truth table, yes.

Grant.

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A "priority encoder" is a thermometer to binary encoder (sorta), the opposite of what you want.

Yeah thought of that, but it gets a bit roundabout for what I'm trying to do.

Never used a PAL, why start now? :) I'll use a PIC though, got some of them to play with. But the PIC is a very different animal to the 68HC05 family I used to work with last century. PIC development and prototype entry is dirt cheap, nice to work with flash memory too.

Hmm, datasheet says up to 1.8V (1.5 typ.) forward on the LED, volts do get a bit high. Two LED chains on a 4052 might be easier if I went that way.

Grant.

will

You mentioned thermometer before? It doesn't ring a bell at all :( Not a 'standard' logic function?

Grant.

"Grant" schreef in bericht news: snipped-for-privacy@4ax.com...

Though I might have missed it, I'm pretty sure the circuit does not exist. Apparently nobody ever needed this kind of circuit badly enough to make the design.

As for a PIC, you need one with enough I/O-pins and outputs with LED-driving capability. As you can go slow, get one with an internal oscillator. Program is less than twenty lines of assembler code. A cheap one is a PIC16F628A.

One problem may arise. When the a, b, c inputs change, two or even three inputs may change at the same time. That's to say about the same time as exactly the same time does not exist. So the inputs can be misinterpreted by the PIC. Your code has to account for that.

petrus bitbyter

Certainly it exists. As I mentioned above, it's known as a "Thermometer Code". It's often used for LED bar graphs. It's not common enough to have a lot of MSI stand-alone parts available, though.

...and that's why. ;-)

No more of a problem than any other asynchronous decoder. If that's a problem then use a synchronous ROM, or any other programmable logic device.

Looks like you can use a LED bar display chip..

Make a latter network with 4 IO pins to create the analog scale for the driver?

LM3915 sounds about right..

reminds me of the GRAY code encoder scheme..

It prevents errors when using position encoders.

Yes, I'm aware of the synch issue with ABC decoder inputs, but the PIC will see up/down error state from window comparator (or sample the analog signal) and do the up/down counter plus decode function. I've got some 28 and 40 pin PICs to play with. Somewhere in the box is a 40k count ADC, so this part is the DAC output to control the hardware in response to the 'real world'.

I'm sort of doing the detail design as I go, need working power circuit that doesn't go up in smoke when I hook it to a pair of 12V 100AH batteries first :)

This one is about third or fourth prototype, at one stage I had a nice 600W ultrasonic oscillator that would cook low ESR caps -- that wasn't quite what I planned for. So now the power circuit is gentler and isolated more from the measurement and control stuff.

Grant.

It is rather the reverse of an interrupt encoder - not sure if they ever existed

LM3915 has LED currrent-limited drivers, as I recall, not logic level.

Grant schrieb:

Hello,

this can be done very easily using a PAl or GAL. I would use a GAL16V8 if they are still available, I just looked into a data book from 1990. As time goes by....

Bye

I was thinking the same thing, and they are still available. We still use them in some older products that use them for memory map decoding. A quick truth table in CUPL or ABEL and you are done. I even think Lattice has a freebie tool set on their website.

Hell. even a small prom would do the trick. Lots of ways to skin this cat.

Yeah, but a 7-bit Gray code typically has 2^7 possible states, not 8.

The above truth table is for a binary (input) to unary (output) converter.