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interface atmega32 with 5 to 32 decoder

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shashidhar1990

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i want to interface 3 to 8 decoder to atmega32 microcontroller to make on the particular LED ? how can it be programmed?:-D
 

shall i get 5 to 32 decoder ic? if , then please update the part number of the IC.
 

send the sequence of 3bit binary to the 3to8 decoder thro atmega port.
(your title gives 5to32 decoder . and message is for 3 to 8 decoder . change them appropriately.)
 

Read this about 3 to 8 decoder.

**broken link removed**

You have to interface the 3 input pins of 3 to 8 decoder to 3 digital output pins of AVR. The you can write values from 0b000 to 0b111 (8 values) to the AVR port and based on the value written to the lower 3 pins of the PORT the decoder output changes.
 
send the sequence of 3bit binary to the 3to8 decoder thro atmega port.
(your title gives 5to32 decoder . and message is for 3 to 8 decoder . change them appropriately.)

thanks, actually i need 5 to 32 decoder . i am not getting a dedicated ic for this, so i am combining 3 to 8 decoder to form 5 to 32 decoder.
 

Here is an example of a 5 to 32 bit decoder made from four 74138 type, 3 to 8 decoders taken from a TTL databook.


138_32.jpg
 
Hi,

If you simply want to light one led out of 32 LED a single AHC138 is enough.
On half as a 2 to 4 row decoder
The other as a 3 to 8 column decoder.
Then connect the LEDS in a 4 x 8 matrix. You need four current limiting resistors.

It may supply up to 8mA while keeping voltage levels, or max 25mA.

Klaus
 

yeah you are rt, i want to light one led out of 32. but in ahc138 we just have 8 outputs. if i connect in 4x8 matrix fashion simply i need 12 outputs(4 for rows and 8 for columns) . still it is possible to then please tell me how to break decoder into two halves? thanks
 

Hi,

Sorry, my mistake. I accidentally thought there are two 3 to 8 decoders in one IC.

So either you use one ahc138 as column driver and 4 extra row lines, making a total of 7 lines.

Or you use two ahc138, one for column one for row. And need a total of 5 lines for 32 LEDS (6 lines for 64 LEDS max).

Klaus
 
If you have 12 available pins on the ATmega32, you could scan a 4 x 8 matrix without using any decoders.
 

Hi,

if you don´t have enough pins you could use a HC595 on SPI (additionally).

Klaus
 

If using a 1 of 8 and a 1 of 4 decoder to scan a matrix of 32 LED's, the outputs of the 1 of 4 decoder need to be inverted, so each scan position has one line high and one line low. Below is an example circuit.



138_matrix.jpg
 

Hi,

Don't forget the current limiting resistors for the LEDs.
Instead of the inverter you could use P ch FETs, like the FDV304P. More driving power.

Klaus
 

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