Hello All,
I am planning to use an analog multiplexer CD4051 (8:1 mux). I have never used an analog multiplexer before, but i have heard that this mux is highly Electro-statically active and requires a Transient Voltage Suppressor before application of any input signals to it. Is it true?
Can anyone please suggest me any circuit or ideas as how to use these mux?

Waiting eagerly for reply,

 

I forgot to mention. My input signal is a noise pattern... typically a radio signal coming out from an aluminum foil. I would like to have a dual supply analog multiplexer, and the voltage range is +-12V. Can anyone please suggest me any valid circuit idea?

 

That is "electrostatically sensitive", meaning it can be destroyed by static charges. I've never amnaged to blow up a CMOS IC, so I don't know about needing major precautions.

Do you have a data sheet? That gives you a lot of information, especially about maximum voltages.

 

Hi,
Thanks for the instant reply. Yes, I do have a datasheet, but they do not mention anything about connections, http://www.fairchildsemi.com/ds/CD/CD4051BC.pdf
You can check this link...

 

Your frequency response is limited to 40 MHz. Can you post the circuit?

 

Hi,
Please check the attached file. I have connected the inputs A0-A7 to inputs and select line is connected to +5V depending on the various conditions in the truth table... like (s0 = 0, s1 = 1, s2= 1)...

Do I need to connect any resistors at the input or o/p?

 

All you need to do is select which input that goes to the output. The nature of the signal sources and the circuit receiving the signals is significant as to the need for resistances.

 

Hi,
Please check the attached file. I have connected the inputs A0-A7 to inputs and select line is connected to +5V depending on the various conditions in the truth table... like (s0 = 0, s1 = 1, s2= 1)...

Do I need to connect any resistors at the input or o/p?

Don't forget to put filter capacitors on the power supply lines near the IC chip. For example, maybe 0.1 uF from Vcc to GND and another from Vee to GND.

 

You need a pulldown resistor for the output, here is the way it is hooked up in my E-Drum project I am working on...

 

Hello All,
Firstly, thanks a ton for the help. It really helped me. I have another doubt. It is regarding the interfacing with an amplifier that I have connected to the further stage. I have connected this amplifier to the output of the mux. Now, when I do not connect the amplifier, I do not see any offset voltage on it, however, the moment I connect the output of mux to it, the voltage at the input of the amplifier gets offset to around 1.5V.
Can anyone please suggest me how to deal with this issue?

 

Hello All,
I observed another this behavior. I tried connecting 1k resistor at the output of mux, but I see that the signal is diminished i.e. i do not see any output at all. however, when I raised the resistance upto 3MΩ, I could see some signal at the output, however, the signal is still offset by 1V.
Later on, I connected a 30MΩ resistor, and I saw that the signal is same as that without the resistor.
What can I do?

 

The MUX is simply a switch. The voltage at the selected input goes to the output. If the output is loaded down then the output voltage will be reduced.

 

Hello Audioguru,
I understand that mux is just a switch. But, when I simply connect the input without the mux, I see normal behavior of the circuit, i.e. it does not get loaded. Its only when I connect the mux, I see the loading effect.

 

Then post your schematic for us to see if it is powered correctly and that the select voltage is high enough.

 

Hi,
I shall do that in. Please check the attachment. All the select lines of 8:1 mux are shorted and controlled by uC. Also, the select lines of 4:1 is shorted and controlled by uC as well.
The uC is working fine. The output of 4:1 mux is connected to an amplifier. I have posted the amplifier circuit in the previous thread.

 

The 4052 will not work properly with its Enable-not pin floating. A low turns it on and a high turns it off.

 

I am sorry, I did not mention that in the circuit diagram, but I do have that pin grounded.
Like I said, each part works very well. The 8:1 and 4:1 mux as a unit and the amplifier as a unit.
However, when I interface, that the time the problem starts.

 

Hello All,
I am still facing the problem. Its been 2 months now I am having problem. Can anyone suggest me any solution?

 

The inputs or output of the analog multiplexers must be biased at a DC voltage that is within their supply voltage range, preferably at half the supply voltage.

 

I fail to see what you're doing with the addressing pins on the 4051 and 4052. If they are all connected together as it looks like they are, you won't be able to select individual inputs - or are the address wires supposed to represent an address buss? You aren't showing any inputs used for the 4051's, except for the address lines, and they are all connected together. With that scheme, only the A0 and A7 inputs could be selected by raising/lowering the uC input to the 4051 address lines.

Similar problem on the 4052; you can only select input from A0 or A2, unless the line to the uC represents a buss.

You have Vcc, GND, and Vee wiring running all over your diagram. This confuses the issue, as it makes the schematic very "busy" and cluttered. Try using Vcc/Vee/GND symbols right at each IC, so the clutter is reduced.

You mentioned earlier in the thread that you were considering using +12v/-12v for Vcc/Vee. The address control inputs need to be able to get within about 3/4 Vcc, so if your uC's output range is 0v to 5v, you will need to use +5v/-5v for Vcc/Vee, or you will need to use level translators.

If you only want AC signals to come through the MUX, you will need to use a cap in series to block the DC level, and a resistor to ground.