DOT display for chain of comparators

[jonnybgood]

I designed a chain of comparators that switch on LED's according to temperature with LM35. The output from the LM35 is amplified by a factor of 10. I managed to get quite close regarding the lighting of each LED with the correct temperature. I now need create a DOT display instead of a BAR display. I know that this is very easily implemented with an LM3914 but my job here is to design it myself. Any ideas or hints? The only thing I thought of is to activating and deactivating tri-state devices that controls the output or each previous comparator by the switching of the present comparator, thereby only leaving one LED lit corresponding to the present temperature. Is there any other method?

 

[barry]

Re: Chain of comparators

You could use two comparators for each dot ('window comparator') such that the comparator turns on only for a range of input values.

 

[chuckey]

Re: Chain of comparators

If you start from a low temp, once the second LED comes on it needs to turn of the first one! So when the third one comes on, it turns of the second. . . . You already have the chain of comparators. . . I think you need to add a SR bistable per LED
Frank

 

[erikl]

Re: Chain of comparators

Is there any other method?

With logic gates you could use the logic scheme of the 8-line-to-8-line priority encoder 74xx149, or a simple RTLogic as shown in the image below for a single LED driver stage:

… where n_ena is the (logic high) enabling signal for the LED "n", and n_plus_1_disa, is (logic high, too) the disabling signal from the next higher priority bit n+1. Only that LED will be "on" which has no higher bit active.

Former schematic & description corrected!

 

[poorchava]

You can use LM3914, which is designed to driver dot/bar display. You can even find application with lm35 + lm3914 in datasheet of one of those (I don;t remember which, though)