interface atmega32 with 5 to 32 decoder

[shashidhar1990]

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

 

[shashidhar1990]

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

 

[srizbf]

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.)

 

[pic.programmer]

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.

 

[shashidhar1990]

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.

 

[FenTrac]

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.

 

[KlausST]

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

 

[shashidhar1990]

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

 

[KlausST]

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

 

[FenTrac]

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

 

[shashidhar1990]

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

yeah rt,. but i dont have 12 free pins over atmega32.

thank you

 

[KlausST]

Hi,

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

Klaus

 

[pic.programmer]

Try this if you AVR has 1 ADC pin free.

https://www.nerdkits.com/forum/thread/1956/

 

[FenTrac]

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.

 

[KlausST]

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