There's nothing wrong with adding a small battery or a supercap to the 4049 circuit. It would take almost nothing to hold the state for weeks or months.
Of late, I have been deeply impressed by the nature of latching relays (aka pulse sequencing relays). But all these devices seem to require an electro-mechanical approach - none are solid-state.
Are there solid-state versions or is it just impossible to make one?
What's so good about latching relays?
1. They don't consume additional power to hold the relay in a powered coil state.
2. They remember their configuration even if the power goes off.
I can think of all sorts of situations where you want micro-controller control, but don't want the circuit to default to another state if power goes down. Oddly, I tried to buy some locally and here in Southern Taiwan they have never heard of them.
Back in my EE days I don't ever remember using them as a form of persistent memory They were mostly used so that a "momentary contact" switch like a pushbutton or in the right circumstances another relay could energize a relay and keep it energized until something else turned it off. Think in terms of push button start and stop switches. I also frequently used them as the core of a "safety" switch. For example if a furnace, etc got to hot the latching relay would set and maintain the alarm even after the temperature went down. It then took a person pressing a reset to turn it off.
One of the first programs I wrote in spin outside of the PE kit labs was a "latch". The idea was to monitor an input and when the input went high it would turn on an output until the input was released and pressed again. Kind of like a start/stop function using a single momentary contact switch.
Too bad your not posting any more, I'm sorry for that.. Don't worry about harassing a healthy debate. There are several pro's and con's and valid reasons for using one solution over the other.
It seems that it you define the criteria to exactly what you are looking for, there is a solution, i.e. "a mechanical latching relay can be pulsed by a microcontroller to completely lock out power indefinitely as a failsafe - including power to the micro-controller - until a repair person examines the unit and submits a pulse to reinstate use. Sure, it is a bit of a suicide pill, but that is a valid use." ... If this is the actual purpose, then why couldn't it be done?.... See attached schematic ... if the LOAD were also part of the supply to the micro then this would also kill power to the micro.
"I just don't see how solid-state can offer that degree of certainty." - debatable ... is G-force involved? Relay's tend to bounce. In this case mechanical would NOT be an option.
"And of course, there is still the question of how to do this with AC power as well as DC. " - This can be solved by using the LOAD in the attached schematic to drive a Solid State relay or simply a triac.
Comments
-Phil
With the addition of an inverter between the Q output and its associated D input, it could also be made to toggle when clocked.
-Phil
Back in my EE days I don't ever remember using them as a form of persistent memory They were mostly used so that a "momentary contact" switch like a pushbutton or in the right circumstances another relay could energize a relay and keep it energized until something else turned it off. Think in terms of push button start and stop switches. I also frequently used them as the core of a "safety" switch. For example if a furnace, etc got to hot the latching relay would set and maintain the alarm even after the temperature went down. It then took a person pressing a reset to turn it off.
One of the first programs I wrote in spin outside of the PE kit labs was a "latch". The idea was to monitor an input and when the input went high it would turn on an output until the input was released and pressed again. Kind of like a start/stop function using a single momentary contact switch.
Too bad your not posting any more, I'm sorry for that.. Don't worry about harassing a healthy debate. There are several pro's and con's and valid reasons for using one solution over the other.
It seems that it you define the criteria to exactly what you are looking for, there is a solution, i.e. "a mechanical latching relay can be pulsed by a microcontroller to completely lock out power indefinitely as a failsafe - including power to the micro-controller - until a repair person examines the unit and submits a pulse to reinstate use. Sure, it is a bit of a suicide pill, but that is a valid use." ... If this is the actual purpose, then why couldn't it be done?.... See attached schematic ... if the LOAD were also part of the supply to the micro then this would also kill power to the micro.
"I just don't see how solid-state can offer that degree of certainty." - debatable ... is G-force involved? Relay's tend to bounce. In this case mechanical would NOT be an option.
"And of course, there is still the question of how to do this with AC power as well as DC. " - This can be solved by using the LOAD in the attached schematic to drive a Solid State relay or simply a triac.