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Trying to make non volatile flip flop circuit

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Chunkymonkey94

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I have successfully made a flip flop circuit using transistor and resistors but I want to make the circuit so that the value is saved when you power down. I know you need something called a floating gate but I don't know how to incorporate this into a flip flop and I do sorta realize that this might be a bit over my understanding but I still want to try it.
 
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duffy

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Did you use bipolar or MOSFETs? It doesn't really work with bipolar, because that requires a constant current. With MOSFETs, and a large capacitor on the gate, and low-leakage design, you can maintain the state that way. For a while. Might want to just use a latching relay if this is for a practical device.
 

crutschow

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Floating gates are usually only available in memory chips such as EPROMS and Flash memory. If you want a non-volatile FF use a CMOS FF and power it up with a battery. CMOS chips use virtually no current in the static mode and even a small lithium coin cell will maintain the memory for years.
 

Chunkymonkey94

New Member
Did you use bipolar or MOSFETs? It doesn't really work with bipolar, because that requires a constant current. With MOSFETs, and a large capacitor on the gate, and low-leakage design, you can maintain the state that way. For a while. Might want to just use a latching relay if this is for a practical device.
Do you mean that the value will eventually be lost?
 

alec_t

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the MOSFET transistor uses a lot of voltages to run doesn't it?
Some do, some don't. Lots are happy with 3V or less.
 

MrAl

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Hi,


I assume that when you want to 'read' the stored value that you must power up anyway.

The way this used to be done back in the age of some of the first computers before floppies and hard drives came along was to use a magnetic memory core. Each cell was made from a small toroid core with two wires through it. When current was put through the two wires in the correct polarity, the core would magnetize in one direction, with current opposite, the core would magnetize in the other direction. This of course provided for a mechanism in which to store ones and zeros (digital data).
To extract the data a sense amplifier was used to detect the change in magnetic state when a pulse was applied. Assuming you have to power up to read the data anyway this wasnt a problem.

Another method which might be simpler using today's technology might be to use an easily magnetized metal with a coil of wire wrapped around it. You could drive the coil with transistors. With current in one direction that would magnetize with one polarity and with current in the other direction the opposite polarity, which provides two states which can be called 'one' and 'zero'.

To read the 'data' (ie magnetic state) you could use a linear hall effect device. The hall effect device will provide a voltage that is greater than 2.5v for say a logic '1', and a voltage that is less than 2.5v for a logic '0'. Thus depending on which direction the current was flowing to the coil prior to power down the stored state can be either a logic '1' or a logic '0'.

This would hold the value for a long time also.

Some CMOS circuits take very little power though, so a small battery could keep it powered up for a long time, thus saving the logic state for a long time. The read circuit would be powered up only when it is desired to read the data, so the battery should last a very long time. This is the way PC computer mother boards maintain some CMOS data and real time clock.

Floating gates are a bit temperamental though, and can change state by themselves with a mere change in temperature. I'd stay away from that idea without investigating the pros and cons thoroughly.
 
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MrAl

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Hi,

Ok, well a bipolar transistor does not have a gate, only a CMOS transistor does.

Can you use magnetic materials/stuff of some sort, like a coil and some metal, or a light sensitive device?
 

Chunkymonkey94

New Member
Yes I could, Does it matter what the coil length is and would you still be using transistors in the circuit or does the coils replace them?
I'm not too knowledgable about these kind of things, I'm still learning.
Thanks for your help! (=
 

duffy

Well-Known Member
Do you mean that the value will eventually be lost?
Yes, the voltage will eventually bleed off.

Carl has a good suggestion - a CMOS flip-flop and a lithium coin cell could hold the state for a couple of years.
 

4pyros

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I have successfully made a flip flop circuit using transistor and resistors but I want to make the circuit so that the value is saved when you power down.
Are you trying to make some sort of nonvolatile memory?
Just what are you trying to achieve?
 

MrAl

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Hi,

The transistors would have to drive the coil. It would probably be an H bridge unless you have dual supplies to work with, then it could be a half bridge.
 

MrAl

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Hi,

An H bridge is a transistor bridge made from four transistors arranged in such a way (like the cap letter 'H') that they can provide for bipolar drive to a device such as a motor (for forward and reverse drive) or a coil.

A half bridge is half of an H bridge, but you need dual supplies or set up some largish capacitors biased at 1/2 of the supply voltage.

BTW, did you ever think about using an EEPROM, or an UVEPROM?
Oh i guess you cant do that can you, with transistors only.

Somebody makes a RAM that is already biased with a battery too, so you can store a lot of bits and have the back up battery built right into the IC socket that holds the RAM chip.
 
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Chunkymonkey94

New Member
Alright thanks for the help, It was very helpful.
The reason I'm trying to do this is only to better understand how these kind of things work.
 

duffy

Well-Known Member
^ Yes, that was my first suggestion for a practical device. There's no shame in it, sometimes a crummy old relay really does beat any other option.
 

MrAl

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Hi,

That's probably the simplest way really. I dont think he wants to use that idea though for some reason. Strange though he said he would use a coil and transistors

^^
o o
 
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