hello.
has anyone experience in multiplexing alternating current ( +/- 20V). i need to switch about a 100 signals so i would like to avoid using relays. i already found some multipexers that can handle dual supply (like the MAX4508-MAX4509). but i am not sure if they are the right choice for this purpose and how to link them up.
grateful for any ideas!
It depends on what current your signals are going to be at.
Generally multiplexing means time division multiplexing but what I suspect you actually mean is matrix switching. That is given N inputs an M outputs you want to switch any input to any output. If so that is not multiplexing.
As I said if this is small currents (10mA or so) then it is a matter of finding the correct chip. If however it is large currents (1A) then it is a different matter.
Although I never used them (4051 was enough for me) I think they are an excellent choice for your project!
Just connect the ABC and common I/O of all chips and chose a mechanism to select the enable chip. This can be done by direct pins (wasteful), by a digital decoder, or - if more that eight are involved by two or three shift-registers 74HC595.
They can easily be cascaded, too. Just make a "tree" by wiring the common I/O of upto eight chips to a 9th multiplexer. Note that the resitance is going up (400Ohms per Level)
thanks for your quick replies. well, here are some further informations about the project first:
switching an array of 64 liquid crystal cells (tn) that are driven with an alternating current that varies from +/-5V to +/-15V. the power consumption will be far below 1mA for each segment.
Since switching of the segments takes some time, i guess time devision multiplexing (like led matrixes) wont work here.
@Grumpy_Mike: so yes, its not multiplexing, sorry. in fact i just need to multiply my I/Os.
@deSilva: i started using the 74HC595s. it works fine! thanks a lot!
so all i need now is some switches to switch the ac - in total 64 switches. i think ill try out the max4509 and let you know...
So yes it looks like the MAX4508 will suite you. Remember you will need to supply it with a +/- 20v power supply.