Real Time Clock?

So what is your opinion about the need for a Real Time Clock on an AutoBrew system? Mine is Arduino, which does not come with one. Software can be used to create real time, but needs to be updated.

I'm not sure you'd need such accurate time keeping.

What are you doing with the controller that you think you need, or could use, an RTC?

Mainly as a timer in case of power loss or surge, that is about all I can think would be needed. In a power loss, I would need to take over the brew anyway.

Battery backup might be a better use of resources.

Probably not necessary but I have one (http://macetech.com/store/index.php?main_page=product_info&cPath=5&products_id=8).

It's I2C, easy to work with.

If you decide to get one, pay attention to the chip; there seems to be a many cheaper models different than the DS3231 which don't have great accuracy.

SMc0724 said:

Mainly as a timer in case of power loss or surge, that is about all I can think would be needed. In a power loss, I would need to take over the brew anyway.

Battery backup might be a better use of resources.

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I don't quite understand what an RTC is going to help you with. So you have a power loss and the system comes back on then what. Are you going to have it log with time stamps periodically in which case you could look at the log and have it recognize that it wasn't done with the previous brew session and pick up where it left off? If you want to do this then you will still need battery backup for the RTC itself to not loose track of time. If you are talking about a battery backup for the arduino I don't know how that will work as you will still need power to turn on your pumps, valves and heating elements.

To handle a power loss I would think it would be more effective and easier to code by allowing you to restart a brew profile at step number x rather than intelligently trying to pick up where it left off.

its probably not intended for a power loss. the internal clock on the arduino isnt fantastic and drifts considerably. however i dont think the drift will be more than a second here or there over the course of a 6-8 horu brew day, which shouldnt be much of an issue. it only becomes noticable if you are logging over the course of a few weeks or more.

crane said:

Are you going to have it log with time stamps ...andy pick up where it left off? If you want to do this then you will still need battery backup for the RTC itself to not loose track of time.

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Yes that is what I was thinking. I planned for the RTC to have it's own battery.

crane said:

you will still need power to turn on your pumps, valves and heating elements..

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I'm thinking that the battery backup would be for the Arduino and possibly the RTC to keep track of where the process stopped, how long it's off, and then allow an intelligent restart.

crane said:

To handle a power loss I would think it would be more effective and easier to code by allowing you to restart a brew profile at step number x rather than intelligently trying to pick up where it left off.

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How would that work? Just log the events, then what happens at restart?

Alternately I could just put a WiFi network connection and use it to log times.

SMc0724 said:

Yes that is what I was thinking. I planned for the RTC to have it's own battery.

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The ChronoDot RTC in my link above has a battery.

jpalarchio,
How do you use the RTC?

SMc0724 said:

jpalarchio,
How do you use the RTC?

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I don't currently. I had it from something else and I don't know that it'll be included in my setup. I plan to log externally so I can just timestamp entries when I insert them into the database.

For the relatively short amount of time a brew session lasts, I can't see it being necessary unless you want to do some kind of timed start like heating up an electric HLT before your day starts.

If you look at the BrewTroller code, they do some nice stuff that maintains the timer during a power fail without a battery or RTC.

SMc0724 said:

How would that work? Just log the events, then what happens at restart?

Click to expand...

I was thinking of making it behave like one of those fancy thermal chambers like we have at work. They have the ability to program profiles where you can ramp from one temp to another hold it for a certain time and loop between steps. I don't think you would want the arduino to just start a brew session as soon as you turn it on. I would think you would want it to sit idle until you tell it to go in which case it could prompt you to enter what step in to profile you want it to start on. That is how all the Thermotron thermal chambers I have used work. You could even have the ability to enter an offset so that you can start x number of minutes into step number y.

SMc0724 said:

I'm thinking that the battery backup would be for the Arduino and possibly the RTC to keep track of where the process stopped, how long it's off, and then allow an intelligent restart.

Click to expand...

if you have a battery backup for the arduino how do you plan to seamlessly switch between the battery backup and your power supply? The RTC chips I have used do this internal to the chip. You simply connect your Battery to the Vbat pin and the power rail to the VDD pin and it will switch over to the battery once VDD falls below a certain threshold. I don't think the arduino has this functionality but i still haven't gotten around to busting out my mega and playing with it so I don't know. You could implement this with FETs but you will need to write FW to monitor the VDD rail to know when you lost power and when it comes back on again. You would also need to have enough bulk capacitance to make sure the arduino doesn't brown out as you switch between power sources.

I use one of these in my Arduino fermentation chamber for datalogging with time stamps:
http://www.ebay.com/itm/New-Arduino...401?pt=LH_DefaultDomain_0&hash=item27c42a2ee9

Works great and has its own backup battery!