Multiplexing Project

Hello this is my first post on this forum, I have a question and I have a diagram which I will let explain my problem [B](assuming you know somewhat about multiplexing)[/B]



Is there any way around not having to have 9 Control Signals?

I'm using a parallel port, so as few pins as possible is better.

Also I should note that this is a very tiny version of what I am trying to do, my actual full idea is the same but with a grid of 128x128 or bigger.

Also each little dot in the grid is a solenoid


thanks

Well, I don't know if is necessary that you must use the paralell port for the project, in my case I'd like to use a microcontroller and then use an I/O expander port IC by I2C bus, in this case I only use 2 pins of microcontroller.

Right, however i'm just using the parallel port for simplicity, but I will replace it with a microcontroller and usb later.

We probably need more detail, such as:

* what it takes to drive these solenoids: voltage, max current?
* what is the timing: how often does a solenoid need to change state, etc?
* what kind of power source will be used?
* anything else that I didn't think of that would influence the design?

But, shot in the dark (and based on the assumption that these solenoids aren't going to need anything faster than, say, 10Hz), how about this:

Each 8x8 cell (or 12x12 or even 16x16) is managed by it's own uController. For the 8x8 case, that would be 8 ports for the 8 rows and 8 more ports for the 8 columns (i.e. the uControllers would need enough ports to cover the number of rows and columns in the solenoid array -- e.g. an 8x8 array would require a uController with 8+8 ports, or 16 ports, plus at least one more for the serial data [two more if you want some sort of data verify or other two-way communication]).

Then there would be a main processor that has one serial line to each cell. It sends array updates to each cell, either simultaneously or one at a time or a few at a time, etc. The cell uControllers would receive that serial data and use it to scan their 8x8 array.

In the case where only one cell is updated at a time (or a few at a time), the main processor could also be coupled to one or more data selectors that would connect one serial port, from the main processor, to a number of cells. So, if it was a 1-to-8 data selector, instead of the processor using 8 lines to update 8 cells, it would only need 4 lines. And actually, because 3 of those lines would be shared by multiple data selectors (i.e. the data line and the three address lines), the port budget would be even lower. There would only need to be one extra line, per data selector, to enable/disable [or select] that data selector.

Now, of course, the outputs of the Cell uControllers will probably need to connect to some sort of driver circuit, as it's likely that your solenoids will require more driving current than the uController can supply (typically 25ma for a PIC [at least for the newer PICs])

I don't know the exact voltage yet.

The timing is somewhat slow, the entire grid of solenoids needs to update once per second, so if by updated or activating each solenoid, one by one, and of a grid of 16x16 then that would be 62.5 milliseconds between each solenoid activating, so number 1 fires, within 62.5 milliseconds before number 2 and so on.


I was just planning on using the signal from the parallel port as a signal and power source, or is that not possible?

Depends on the solenoid, but most require much more current than could be supplied by most parallel ports.

Also, do the solenoids need to be held in state, or just pulsed?

And when you say "parallel port" what do you mean? The parallel port on an old PC (or new PC with a parallel port PCI card installed) or on a uController or is this some sort of exotic wine that when imbibed leaves you beside yourself?

You really need to give us more information.

The solenoids don't need to be held in one state, they they just pulse once, then a tiny spring will push them back to there "off" state.

I mean a old PC parallel port, like the old printers used. for now the later I will switch to a microcontroller.

What if I used a series of 74HC595's and chain them together?

Possibly. But, for something as large as a 128x128 array, for a 1 second update cycle, that leaves only 61µS per solenoid -- not sure if that is long enough to activate it.

But, if it turns out it is, I would use two sets of '595s, one for rows and one for columns. Then serially clock one bit down each chain. The row bit would be advanced one clock (then latched) after the column bit has been advanced along one full row. When the bit "falls" out the far end of the serial chain, start another bit at the beginning of the chain.

Another way would be to divide the array up into smaller blocks, as you proposed at the beginning. That might work very well. But you are still, more than likely, going to need drivers on the outputs of the '595s, no matter the configuration.

I don't know what happened to my comment I just posted, I cant remember what I typed completely.

what are drivers? are they where external power is connected along with the outputs of the 595's?

Hu-wee -- That's a large subject -- sounds like you might be biting off more than you can chew - son.

But if you're game:

* http://stevekulpa.net/pinball/bally_soledummies.htm (those transistors should have resisters on their bases)
* http://www.edn.com/design/components-and-pack...le-solenoid-driver-is-adaptable-and-efficient
* http://electronics.stackexchange.com/questions/62415/solenoid-driving-circuit
* http://ruggedcircuits.com/html/circuit__7.html
* http://ruggedcircuits.com/html/circuit__19.html

So is it basically just a resistor or transistor between the output and what it is that your controlling?

OK, this is all based on a big assumption -- the assumption being that the solenoid is going to require more power than the shift register outputs or uController output, or data selector outputs or the output(s) of whatever device is being used to multiplex or otherwise get the signal to the solenoid, can deliver. A 74HC595 output can only source around 8ma and sink around 6ma at VDD = 5V. So, if your solenoid needs more than 8ma to move the shaft, then a 74HC family output won't be able to do it.

So, you need a driver (basically a specialized amplifier). One way is to use a transistor. A PN2222a can sink up to 1 amp of current. But, there are solenoids that require more than that, so to drive one of those, you would need something beefier. And then there's the issue of whether or not your solenoid is AC or DC and how much voltage it requires, etc.

A PN2222A is good for 40 volts, max (and more like 20 volts -- to allow for noise spikes and such). An MPSA32 has a 300V breakdown voltage, so probably useable to around 200V.

Like I said, a lot to know, hard to cover it all in a forum post -- you kinda need to do the work of learning the basics -- i.e. pay yer dues

He could use charlie multiplexing but his diagram doesent make sence to start with even if he is using parrallel port but that just initial inspection

@steve: that actually makes, sense I thought that's what it was, I should note: instead of using solenoids I will be using ferrofluid to make tiny valves. Yes the solenoids were going to be used as valves, however, they require to much material and to much time to make, considering that I would make them myself to get the size I need(1/8 of a inch)

However the ferrofluid valves, still require a electromagnet.

So, you need to determine that is needed to drive those electromagnets:

* Voltage?
* Current?
* Min pulse time?

And also be sure to include a diode to protect your circuitry (the 1N4001 in the following [I would use a 1N4004 or better]):

* http://www.jaycar.com.au/images_uploaded/relaydrv.pdf

Id use opto couplers as well if I were you otherwise I can see one transistor going short or what ever driver you are using one nasty bit of current being transferred to the printer port or micro and one big enormous bill for a motherboard or damaged cpu plus I would also use opt couplers for another reason and that is to prevent noise upsetting registers if you are using micro's and or false readings if you intend to read back from the port but that’s general advice to you found by non other than shear hard experience

Up to you I like to make life easier not harder but i think that will be in a waste of time too judging from what I’ve come across so far which doesn’t look very promising

Be carefull check the datasheet

Maximum output current sourced by any I/O pin
....................................................................................................25 mA

Which means 8 pins 8 multiplied by 25ma = what Steve ? Which exceeds what steve max porta or port b current which is only 100ma max "Be carefull"

Quoted word for word from none other than datasheet on pic 16f88/ 84


Maximum current sunk by PORTA........................................................100 mA
Maximum current sourced by PORTA........................................................100 mA


Maximum current sunk by PORTB....................................................100 mA
Maximum current sourced by PORTB .................................................................100 mA

What else Steve parrelel port current is what Steve ??

The output of the Parallel Port is normally TTL logic levels. The voltage levels are the easy part. The current you can sink and source varies from port to port. Most Parallel Ports implemented in ASIC, can sink and source around 12mA. However these are just some of the figures taken from Data sheets, Sink/Source 6mA, Source 12mA/Sink 20mA, Sink 16mA/Source 4mA, Sink/Source 12mA. As you can see they vary quite a bit. The best bet is to use a buffer, so the least current is drawn from the Parallel Port. (in otherwords keep this to apsolute minimum you can see why cant you ) Now you can

YOU must check the datasheets acc your motherbourd and I would still isolate via optocouplers Its better to be safe than sorry

Sorry is too late motherbourds are pretty expensive and and you not only riusk mother board you also risk cpu on motherbourd I5 or I6 OUCH !!

Then time to re install software very expensive especially after you have to do all the updates to go alongside this thats another 8, 9 hours these days

Who pays for this hmmm ?? One expensive mistake

and its whoopsie I cant use my pc today because its in the repair shop and its whoopsie Ive just lost all my accounts and got the tax man on me and its whoopsie Im suing you for loss of eranings and its whoopsie Ive just lost all my bussiness emails and its whoopsie

You think Im joking no , no no no no butter butter but but but ! Oh yes all clever stuff this You wait

All dead simple all this ho ho all very simples

Think !!

Good point! Definitely use Opto-isolators on the parallel port. Better to blow out one of those, rather than the parallel port drivers on your motherboard!

I was speaking in terms of his final goal, to run this thing from a uController [not the parallel port of a PC -- he's only doing that in the preliminary development phase]. Also, it may not be the parallel/uController outputs that will ultimately be driving the solenoids.

But, I agree with using opto-isolators on the parallel port during that preliminary development phase Regardless of what is actually driving the solenoids.

Except, only one or two ports will be "on" at a time, so actually no more than 50ma at once?