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one bit of memory?

According to your circuit schematic, your comparator has negative feedback. That means it isn't acting as a comparators, it's acting as an (uncompensated) opamp. This may well result in oscillations.

Here is a circuit that may work. It's a starting point for some experimentation anyway. It's a flipflop, with the comparator used to increase the impedance of the output. If your comparator is open collector, you may need a pullup resistor on the output.

VCC=9V .------------------o-------o-----------. | | | | | | | | .-. .-. .-. | | |100k 100k | | | |47k | | | | | | | | '-' '-' '-' | | | | |\| | o-------)---------|-\ Output | ___ ___ | | | >------. From 555 o-|___|-. .-|___|-o---. o-----o---|+/ | ___ | 1MEG | | 1MEG | | | | |/| | ->|--|___|--o----)-------o | |/ | | | ___ | 100k | \| '--)-----| | | '---|___|-----' | |--------' |> | | | 1MEG ---

Reply to
Robert Monsen
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-- Regards, Robert Monsen

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Reply to
Robert Monsen

In my ongoing quest to waste as much time as possible on my silly phone gadget

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I added a circuit to "remember" if the phone ever rang so I can turn on a flashing LED as a "missed call" reminder.

For memory I used the LM339 as OR-gate sample circuit from the NS pdf spec sheet, and fed back the output as one of the inputs with the output from the 555 timer being the other input.

This worked great till I decided to switch to the much lower power LM339 near-compatible TLC3704 chip from Texas Instruments

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Apparently the push-pull outputs work differently enough that the initial power-up state of the chip is "on" rather than "off", so my one bit memory circuit doesn't work with the new chip very well (but I don't want to go back to the 339 because overall the new circuit uses a lot less power than the old one and I don't need pull-up resistors all over the place).

Anyone have any suggestions for a nice low power way to provide the one bit of memory I need? Or maybe a way to hack around the initial power-up state so I ignore that particular bit of feedback, but notice it later when I really want it?

(Of course if I really wanted to save power, I wouldn't add all this extra junk anyway - the important bits seem to be working fine and only draw about 0.5mA - about 10 times less than the first version).

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Reply to
Thomas A. Horsley

An SCR. Once triggered, it will continue conducting until power is removed from the anode, at which point it waits for another trigger.

Or for more complication, use two transistors as a flip-flop.

Michael

Reply to
Michael Black

Rge SCR sounds good - I found a web page describing them with an example equivalent circuit, and it looks like two transistors setup as a flip-flop (or really just a "flip" :-) is the same as an SCR. I'll have to play around with some things and see if I can get it to work.

Thanks.

Reply to
Tom Horsley

That means it isn't acting as a comparators, it's

Yeah, I think I noticed I got the diagram backwards, but the actual breadboard has 'em hooked up the right way.

Thanks. I'll play around with it and see what I can get to happen.

Reply to
Tom Horsley

Just to let the folks who provided suggestions know, everything is working now. The new and improved web page has the gory details:

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Thanks for all the help! (Now I just need to decide on the mechanical design and get a new box of some kind built and get the circuit board all laid out and put together - heck I can still waste weeks on this thing :-).

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Reply to
Thomas A. Horsley

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