Multiplexing project

[BeerBelly]

You will need 16 595's. 8 for the rows, and 8 for the columns.

128 by 128....You are going to need 32

 

[ChrisP58]

128 by 128....You are going to need 32

Yes, you are correct. I shouldn't do binary math in my head this late at night while watching TV.

 

[throbscottle]

do you mean a ferrofluid actuator to control the fluid for what I need?

It's a thought to play around with - ferrofluid will change shape when you put a magnetic field close to it, and could potentially do away with a world of fiddly little mechanisms if you have the right container for it. I was thinking of some kind of little plastic bubbles full of it, if you have the means to make them. Depends on your budget whether you can do this kind of experiment - it's expensive stuff, apparently.

 

[mrn]

@BeerBelly: what is the output voltage for the 595's?

@Chris: so by having seperate data lines for the rows and columns, it would save time by not having to wait till all 128 slots are filled?

@throbscottle: That is a good idea, however can the fluid change shape that quickly? can it return to fluid state after the magnet force is gone?


this might be helpful I decided to scale the design down to just 64 by 64 for now to save on materials and what not.

So I will only need 16 595's

 

[BeerBelly]

@BeerBelly: what is the output voltage for the 595's?

4.5 to 5 volts
Data sheet https://www.mouser.com/ds/2/302/74HC_HCT595-225040.pdf

 

[mrn]

@BeerBelly: So that should be plenty then right? I tested a tiny U shaped wire with a 1.2 volt AA batterie and got a good attraction.

 

[BeerBelly]

@BeerBelly: So that should be plenty then right? I tested a tiny U shaped wire with a 1.2 volt AA battery and got a good attraction.

No, The voltage is high enough but 4ma is not nearly enough current.
With the voltage running through your loop while the loop is actually doing work, measure the current with a meter. Double that for reliability. This is the amount of current you should allow for.

A wild guess, 4 amps.

 

[ChrisP58]

Driving both the row and column string at the same time cuts the total update time in half. Each string still needs 128 (or 64) clock and data bits.

Like BB said, the current is the real question. Even with a low voltage, a short piece of wire can draw several amps, due to its low resistance. And, if you were testing with a AA battery, the actual voltage delivered from the battery during the test will have been lower than the 1.2 open circuit volts. Probably significantly lower due to the internal resistance of the AA battery.

For an electromagnet, magnetic strength is a function of AmpTurns. A coil of 1 turn drawing one amp will have the same magnetic strength as a coil of 10 turns drawing 0.1 amps. The reason most electromagnets, such as solenoids and relays, have many turns, is to use as little current as possible while still having sufficient magnetic strength to get the work done.

In your case, the ideal coil will be optimized to run at ~5 volts. Design your coil with however many turns gives you the strength you need, while drawing as little current as possible. Only when you get to that point will you know whether you can drive the coil directly from whatever logic you choose, or if you need to buffer the logic outputs with transistors.

Notes:
- The current in a DC coil will be a controlled by it's resistance and the applied voltage as per Ohms Law.
- You can run your logic circuits at a voltage lower than 5V. This will mean fewer turns in your coils to still be optimized for the working voltage. 3.3 Volts is a common level, but the HC595 claims to be usable down to 2V.
- While resistance is the dominant factor for DC current, if you are driving the coils with short pulses, the inductance of the coils may also be a factor in limiting the current.

 

[BeerBelly]

Good information Chris posted.

When optimized, solenoids and motors get smaller with higher voltages (for the same power output).
Although that may not be applicable in your situation.

 

[mrn]

I will test the current, on the wire loop, also if Im reading the data sheet right, the medium voltage supply for the device is 5 v?

the wire and magnet valve seems like the best idea so far however, I don't know if it can seal off fluid.

I like the ferrofluid idea, I might do something like that, I don't know if this will take more or less voltage/current.



SIDE NOTE:
So good news, I just made working ferrofluid at least a form of it, I just used iron oxide and a magenet and it works great!

I made the iron oxide from just some washers in water attached to a battery.

 

[mrn]

So i'm thinking in order to have such small electromagnets I will need quite a bit of power, more then 5 volts, how would I go about doing drivers?

I they just transistors? when one gets a signal it switches on the external power?

 

[ChrisP58]

How much voltage, how much current, and what's the pulse timing?

If 5V is enough, then you can increase the current with a simple transistor circuit. If you need more voltage as well, then the circuit is more complex.

 

[BeerBelly]

Yes, darlington transistors or logic level mosfets.
The ULN2803A is an interesting IC It has 8 darlington drivers with spike suppression diodes in the IC. I don't have a lot of experience driving coils with the newer ICs but I would give this IC a try. They cost about $1 each.

Link;https://il.mouser.com/ProductDetail/STMicroelectronics/ULN2803A/?qs=sGAEpiMZZMutXGli8Ay4kAHmCxIxFTXSfbpCT5ik4XI%3d

 

[mrn]

@Chris: well what ever the parallel outputs but for external power for the coils, i'm guess around 8 to 11 volts, i'm not sure about the timing, i'm not even sure what the technical term for the timing is. I know microseconds but i thought there was a different term for it, something with a μ, pardon my noobieness here

I will have to come up with a coil that does what I need, then I will supply the info on the current and such.

@BeerBelly: so the ULN would replace the 595's or go along with it? they are more or less expensive then the 595's but if ULN's can handle the voltage that I would need drivers for, then the ULN's would save allot of money, not having to buy all the transistors.

 

[BeerBelly]

The ULN2803A would not replace the 595s.
The ULN2803A is designed to drive and provide the protection diodes necessary to drive 8 relays. In your case coils instead of relays. This IC may not provide enough drive current for your needs, that is something you will have to determine through experimentation.

 

[alec_t]

You would, of course, need 512 of those ULN2803's for a 64 x 64 array of coils.

 

[mrn]

@BeerBelly: oh ok, maybe it would be cheaper to just use transistors then?

@alec: couldnt I just have 16? because I would only be applying power to the pos and neg of the grid?

 

[BeerBelly]

You would, of course, need 512 of those ULN2803's for a 64 x 64 array of coils.

Yes you could do it that way, and use "and" gates(diodes) at the matrix points. I think the cheaper and more compact way would be to find or build a PNP equivalent for columns.
For a 64 x 64 array
ULN2803A for rows..................8 ICs
PNP or MOSFET equivalent for columns.....Unknown...maybe 16 quad motor driver ICs

Most printing type devices use just a row and move the print head or printed material up/down to provide the column function.

It's an ambitious project. I'd like to see it when some progress in made.

 

[BeerBelly]

@BeerBelly: oh ok, maybe it would be cheaper to just use transistors then?

Each ULN2803A would replace 16 transistors and 8 diodes and quite a few resistors

 

[ChrisP58]

You might be able to use 8 of the ULN2803s in place of discreet transistors for the negative edge of the grid, but not for the positive edge. There you will need PNP transistors, or p-channel mosfets. If you need more than 5V there, you will also need level shifters.

I am not aware of a PNP version of the 2803 family. I do use a lot of single and dual digital transistors, which are BJTs with internal bias resistors. They come in NPN, PNP and NPN/PNP pairs.