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[SOLVED] ON/OFF controller IC with retaining its state after power resume

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Raguvaran

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I am designing a smart switch. i need a on/off controller IC which should retains its present state. If power fail while switch is ON or OFF, after power resumes, the ON or OFF state should be retained.

I found many on/off controller IC in internet. But i can't ensure that it retain its state.

For designing a smart switch, small foot print IC is required. Now i am using Microcontroller with EEPROM. I hope this on/off ic will reduce the cost of the design and avoid programming.

kindly guide me.
 

BradtheRad

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Possibilities for storing status during power-off:

* A one-bit 'core' computer memory. A tiny ferrite donut has wires going through it. Magnetize it by a pulse of current. One polarity means 0, the opposite polarity means 1. To read its state, send a weak pulse and detect the amount of current which the donut permits to flow.

* A CdS photocell (light dependent resistor) has a movable shade over it, which either darkens it or else exposes it to light. Attach a magnet to pull it back and forth by small solenoid. This strategy assumes ambient light is available at power-up.

* A latching relay. It's different from a plain relay. The latching relay changes state when you apply a short pulse of current, then holds that state indefinitely until you apply an opposite pulse of current.
 

betwixt

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EEPROM is by far the easiest method to use. Just read the state when powered up and set the switch accordingly. When the switch setting changes, just write it back to EEPROM. If it is a smart switch, I assume it already has an MCU with EEPROM to hold its ID so you don't need an additional IC.

Brian.
 

Raguvaran

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I am using esp8266 in backend. Now I am using attiny13a for each switch. Every switch is connected to esp8266. If esp8266 fails, atmega13a act independently as manual on/off control switch. I thought to use a on/off controller ic, so that even esp8266 fails, on/off controller IC act independently.
 

Raguvaran

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Thank you for reply. I think Latching relay is suitable. I will check about it.
 

doraemon

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Hello!
You don't really explain what you want to do, so it's not easy to reply. If you mean that you want to memorize a state,
then there are myriads of solutions as explained above. EEPROM, FLASH, FRAM, etc. And if you want a simple switch
(on / off), then you may consider using... a switch. Rocker switch or anything like that, which has 2 stable states,
and that wouldn't change with power off.
Dora.
 

c_mitra

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Thank you for reply. I think Latching relay is suitable. I will check about it.
There are very simple reed relays that stay latched in their current state indefinitely.
 

Raguvaran

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Sorry for my explanation before. I am using a capacitive touch sense (TTP223) for switch. I not use any mechanical switch. currently i am using ATTINY13A to capture the touch through TTP223 and store the state in EEPROM. In back end esp8266 manage the network. ESP8266 control the switch through its GPIO. If esp8266 failed due to any reason, the switch can work in manual mode because of ATTINY13A.
In view of cost factor, ATTINY13A is costly compared to on/off controllers. As my search in internet, ATTINY13A is only microcontroller with small footprint and EEPROM. Only to store the on/off state, EEPROM is required. So i thought to replace ATTINY13A with a on/off controller that retain its state after power resume.
 

KlausST

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Hi,

There are cheaper ATTINY than the ATTiny13A.

Why don´t you replace the TTP223 with an ATTINY?
With a bit of software the ATTINY should be able to detect capacitive touch.

Klaus
 

c_mitra

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Hope this links will help for others too.
You need battery backup or a microcontroller with EEprom.

Using a microcontroller with storage may be a smart idea but surely an overkill. The power supply for the microcontroller may be more expensive than the microcontroller itself.

It can be quite useful if you have several keys that are controlled by one microprocessor.
 

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