F/F Circuit

Read recently that they'd made mram-based flip flops, which retain their state when powered off. Can't find them with a quick search, though.

You could match that with a reset controller chip to get a clean edge once the system is powered up.

Freescale

This is what came to my mind:

Can you use a mechanical device? A motor driven cam or something like a car door lock solenoid, with switches & logic to determine direction?

A mechanical setup has the disadvantage of slow speed/large size, and the advantage of retaining the last "setting" forever without needing power.

Ed

Use a PIC, and save the state in EEPROM if you don't need more than

It's probably not the way to go and we will never know if you don't tell us what you're really trying to do...

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A mechanically latching relay would work, as would storing the last state in non-volatile memory, such as EEPROM or FLASH. -mpm

Why a 555? Did the teacher say so? Because that's not the chip you'd use here, unless you're looking for a one-shot to generate the toggle pulse.

You should ask the teacher why he/she wants to use a 555 here, and report back.

Good Luck! Rich

You can buy relays that do this (alternating relays), which are used for load levelling on machinery (among other things). They are big, use a lot of power, and cost a fair bit of money, and have a limited life.

If you want to do it at a chip level, the microcontroller suggestion is a good one, parts cost will be minimal, and only a few parts required (an external reset circuit may be called for). Lifetime is somewhat limited, still *far* better than a relay, and can be improved by additional orders of magnitude by clever programming to load level erase operations on EEPROM cells. Not difficult to do. The same thing could be implemented with a battery-backed CMOS FF (eg. 4013), with more parts. In either case you'd have to reliably detect and debounce power state changes. Some of that can be done in firmware with a micro.

Best regards, Spehro Pefhany

Spehro Pefhany wrote:

Many other things--with much lower specs.

Maybe the magnetic latching relays you have seen are. The ones I've seen are tiny.

A tiny pulse is typical of the ones I've seen.

DJ's MRAM suggestion makes a bistable relay look cheap.

Yup.

Those are *latching* relays, not *alternating* relays, so they do need some circuitry to control them. An alternating relay could be used as-is.

Lots of latching relays. Eg.

Best regards, Spehro Pefhany

Ramtron does such a product (FRAM obviously)

Robert

Yes! That was it. Thanks!

Robert ... could you please check your link. This sounds like it may be just what I need, but your link doesn't work. Anxious to hear from you. Thanks.

west

Never mind Robert, I found the info using part of your link. I immediately see a problem in that this FRAM is a sofisticated surface mount chip. All I need is 1 logic level out. Also, I don't have experience in surface mount. Do you know if this chip comes in a dip 14 or equiv package? Thanks.

west

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I am now studying latching relays. If I go that way I need to find a small one. The criteria again is : power on gives a logic low; next power on gives a logic high. IOW shutting the power off does not change states.

west

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Hi Arlet, I always wanted to learn about PIC. Perhaps you can recommend a good beginner's book. I do have some basic electronics experience.

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I tried to make my requirements as simple as possible with only a logic state that toggles with each power on. Why do you require to know what goes on after that? I don't even know until next semester.

west

You're probably right, Rich because a general purpose F/F may also work.

west

If it's not on their site I doubt it, Surface mount isn't hard to work with though and most newer chips no longer come in DIP packages so it's worth learning how to deal with them.

Robert