1
\$\begingroup\$

I have been playing with this multiplexor recently: 74HC4051.

I have been searching all day for an alternative version where it is 4 channels instead.

My task is simple and perhaps I am using the wrong component which is why I can't find a low-cost component that allows me to do this.

I have 4 LED and 4 transistors. My scenario "processor" has 2 digital inputs,

My task is to switch each transistor at a time, in turn, the LED will be switched on.

Is a demultiplexer the correct component for this? Any help is appreciated, I am quite new to hardware design and am trying to learn about the different types of components available.

What options are available?

Thank you very much for your time!

\$\endgroup\$

3 Answers 3

2
\$\begingroup\$

No one is forcing you to employ all the functionality of the 74HC4051, you can simply ground the most signficant address input S2 and control the other two lines S0/S1 (as well as grounding or controlling /E). Just ignore (leave open) Y4..Y7.

Is it the best chip for the job? Perhaps not, but it will work fine in many circumstances. For example, a 74HC138 could be used to drive PNP transistors (active low), but the 4051 actually requires fewer parts because you can use a single resistor and choose to use either PNP or NPN transistors.

\$\endgroup\$
2
\$\begingroup\$

This multiplexer is bi-directional, essential for your question as it's unclear whether the 'processor' is reading or controlling the transistors.

Alternatives in that family are 4052, which is two 4:1 muxes with common select inputs, and 4053 which is 3 fully independent 2:1s.

If the processor is controlling up to 8 peripherals, then the more usual way to do it is with a single directional logic device like a shift register, 595 is popular. You use 2 or 3 processor pins to load it with data, which is then available on all 8 output pins at the same time. With appropriate control, any pin can be manipulated independently.

\$\endgroup\$
2
  • \$\begingroup\$ Hi, the processor has 2 GPIO lines that can go high/low. Does this change your answer? I did stumble upon the 74HC4052, however, it is dual. Wondering if there is an IC out there with 1 circuit 4:1. \$\endgroup\$
    – ADL
    Commented Nov 12, 2016 at 8:23
  • \$\begingroup\$ How much current do you need? I ask because a lot of µCs out there can happily drive 20mA on their IO pins and you could connect two LEDs in an antiparallel fashion to one pin and don't need a demultiplexer at all. \$\endgroup\$
    – Janka
    Commented Nov 12, 2016 at 8:46
1
\$\begingroup\$

When I did this in '74, I had 4 different solutions for this with no need for a micro.

  • An up/down counter with a 1 of 8 decoder and enabled sequence in both directions.
  • a parallel in/out (PIPO) shift register with a timer to // load a pattern such as 1000 then use last port as serial input and use Schmitt inverter gates to create a 1 shot LOad ENable pulse then a 1Hz clock for SHIft INput
  • A Johnson counter is the most popular choice as this has the counter decoder built in and you can truncate up to 10 counts by using any output to reset back to the 1st position.
  • A serial in parallel out (SIPO) shift register with a circulating serial input

  • transistors should not necessary with 74ALxx or 74AHCxx or even 74HCxx series, but perhaps a small R based on voltage drop in CMOS, LED and Vcc to drive 10~15mA. IN most cases from 5V the 2 or 3V rise is harmless from an Vol signal.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.