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I have a a 8-to-4 Multiplexer ICs (MM74hC4052N) and I want to use it as a 8-to-4 encoder or 8-to-3 encoder.

Is that possible? If it is, can drop me some hints on how to do that?

At one glance, I thought this 8-to-4 Mux works by taking inputs (in this case, 8 inputs) and using the select signal, it channels the inputs simultaneously into the 4 outputs.However, after reading the data sheet, I was getting confused. The truth table does not follow what I thought.

Practically, I have 8 switches representing 8 bits of a binary number, and I need to send a 4 bits signal to a microcontroller, representing the 8 bits binary number, using this 8-to-4 IC.

Link to datasheet : http://www.farnell.com/datasheets/89046.pdf

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From 8 switches you should get a 3-bit signal, unless you are looking for some redundant coding scheme. The appropriate 74-series part would be the 74148... –  Brian Drummond Jan 17 '13 at 22:21
    
that would be the ideal case. But I'm stuck with this ICs at this moment –  CacheMemory Jan 18 '13 at 9:19
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1 Answer

First of all, the 74HC4052 is not an 8-to-4 multiplexer, it is a dual 4-to-1 multiplexer with common select inputs.

If I understand correctly, you want to connect a total of 8 switches, four at a time, to your microcontroller. You would need two of these chips in order to do that.

However, you could connect them two at a time to your microcontroller with just one of these chips.

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Actualy, it is not the switches to be connected to the microcontroller, but merely a coded 4 bits representing one of the 8 switches –  CacheMemory Jan 17 '13 at 21:20
    
In that case, this chip is not a good fit for the application. It would actually be easier to have firmware on the microcontroller read in the switches two at a time and then encode the value, than to build a hardware encoder with this chip. –  Dave Tweed Jan 17 '13 at 21:47
    
I just figured it out.. If I connect 4 switches at the inputs (of 1 4-to-1 Mux) that has 2 outputs (pick one out of that two at a time) and 4 other switches with the same configuration, I could actually have 8 switches encoded into 4 bits. 4-to-1(one out of two, the non active is LOW) 4-to-1(one out of two, the non active is LOW) Then it hits me, can I make the the output of MUX both 0? checking the Truth Table, I then found out that both Mux are sharing two input A & B, and not 2 pairs of A & B, and thus the implementation is not possible.... Is this correct? –  CacheMemory Jan 18 '13 at 3:33
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