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1  Using Arduino / Sensors / Re: Adjusting calibration based on temperature, how do? on: January 22, 2012, 05:42:55 am

Brown is the beer, the thin grey tube is the temperature sensor. The thick grey tube is hollow, but sealed at each end, at the top end by a solid wall, at the bottom end is a latex diaphragm(the black thing). I'll measure the air pressure inside the thick grey tube. The volume of the cavity under test will in reality be quite small, but it will be at the end of the long tube, so as to make it possible to hold it at the bottom of the vat.

How much of a difference do you think the beta value will make? If I set it at somewhere halfway between water and alcohol, how far out will that throw my readings? By the way, I will be calibrating as I start each brew using my glass hydrometer, and after the brew has reached its fermenting temp, it will stay pretty much at that temperature.
2  Using Arduino / Sensors / Re: Adjusting calibration based on temperature, how do? on: January 21, 2012, 09:33:28 pm
Your first problem is that beer in ferment is a "live" variable

This is the variable that I'm wanting to measure, the calibration that I'm talking about is at one instant, so I know the temperature and the density of the liquid at that temperature, and from there I want to figure out what the temperature would be if it were at another temperature. The point of the exercise of measuring density while brewing is to determine the rate and amount of change in density, but to do this you normally have to read at a particular temperature.

Also, not much effervescence, if any, builds up during the primary ferment. The CO2 is released into the atmosphere through an airlock.

The vessel whose pressure I will be measuring will actually be a tall thin tube with a diaphragm over one end. This end will be held about 2cm from the bottom of the vat, and the sensor will measure the air pressure in the thin vessel.
3  Using Arduino / Sensors / Adjusting calibration based on temperature, how do? on: January 21, 2012, 04:29:05 am
I"m working on building an Arduino hydrometer for measuring the specific gravity of homebrew beer. So far, I've decided on measuring the head pressure at the bottom of the tank and mapping that against my glass hydrometer. The question is, how can I use a temperature reading to figure out what the specific gravity of the brew would be if it were at a predefined temperature, even if it is not, in reality, at that temperature.

For instance, let's say the predefined temperature (call it set_temp) is 22 degrees celsius. I take my pressure and temperature readings and discover that the gravity is 1.028, and the temperature is 27 degrees celsius.

The gravity of the beer at 27 degrees will be different to the gravity at 22 degrees. How can I use the temperature reading to figure out the density at a particular temperature?

Is that clear, and does anyone have any ideas?
4  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: January 20, 2012, 07:46:24 am
After working on other things for a long time, and burning out my INA125p chips, I've finally gotten back into this. Ordered new chips in the mail. I've decided to go with a DP pressure sensor, which will read the pressure b=behind a diaphragm stretched over the end of a tube, which will be put into the brew and held at a set depth. This is essentially the same as the load cell idea, only it measures the effects of the density change in a different manner. When I have a prototype up and running I will let everyone know what goes on.
5  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: August 22, 2011, 04:18:55 am
Yeah, that's probably the case, but I'm happy with a ball-park idea. The original plan was just to notify me when the beer has stopped fermenting for three days, and given that the brew will stay within 2 degrees of a particular temperature, I reckon it should be good enough to do that, even if it can't give me an accurate alcohol content reading. Also, the scales my load cell came from were accurate to 0.01g, so I feel I should be able to get close enough for what I want to do.
6  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: August 21, 2011, 05:59:57 pm
Aah, I get you. I was thinking that you meant measure the increasing pressure caused by the release of CO2 into the tank, but the airlock is designed to prevent this buildup. That's a good idea though, and I think I have a DP sensor lying around somewhere too. I'll keep working on the load cell option for now, because I want to avoid putting holes in the body of the vat, but if it doesn't work out, then I'll give the DP a shot. Thanks Lefty!
7  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: August 21, 2011, 05:39:17 pm
The ina125p instrument amplifier came in the mail just the other day, and I had a little play last night, but I have nothing worth reporting yet. I like the pressure/volume solution, but airlocks will negate the pressure value after a certain point.
8  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: July 17, 2011, 07:25:06 am
Thanks guys, this is a really good idea. I had been thinking along the lines of using an existing sensor and figuring out an interface, but this is much better. I have a load cell from some scales in front of me as I write, and will do some prodding this week. I'll post my findings. Thanks again!
9  Using Arduino / Sensors / Re: Specific gravity sensor, any ideas? on: July 15, 2011, 08:26:39 am
@Graynomad. Yeah, I was thinking of a tube open to the brew, I hadn't thought of using a rangefinder though, I can't think how I missed it now that I think about it. I'll have a think about that one.

I had a brief look about, and alll the options that I saw for buying sensors were wither too expensive or too annoying to interface to an arduino (I'm already using one for temperature control, might as well just add to it), or both. I'll keep looking though. One that I saw uses a hall effect sensor, which may be another option.
10  Using Arduino / Sensors / Specific gravity sensor, any ideas? on: July 15, 2011, 07:43:27 am
Hi there, I'm trying to find/build a specific gravity sensor in order to measure fermentation in my homebrewing setup. Does anyone know if such a beast exists?

If not, what do you reckon is the best way to interface an arduino to a hydrometer? I've thought of using a potentiometer with (ideally) zero physical resistance, or a light sensor array to sense the location of the highest point on the hydrometer. If I go along this route, I need millimeter accuracy, so I'm not sure how easy the light sensor option would be.

Brainstorm time.
11  Topics / Science and Measurement / Re: Brewing thermostat on: July 07, 2011, 08:24:37 pm
I was using a switchmode regulated 12v power supply, feeding directly into the 7805, I'm now using the supply's equivalent in 5v with no regulator, works fine.
12  Using Arduino / Programming Questions / Re: if statements, something going wrong on: July 06, 2011, 08:32:34 am
In the end I managed to get it going, it was indeed the case that alarm_off == 1 wasn't true, but that's sorted now. On to bigger problems...
13  Using Arduino / Programming Questions / if statements, something going wrong on: July 06, 2011, 02:30:37 am
Hi there, I'm building an alarm clock, and I've come across an annoying problem, I assume it's my fault, but I can't figure out what might be wrong. Any help would be greatly appreciated.

Essentially what I'm doing is taking the time from a DS1307, that bit works fine. Next, I'm using two potentiometers to set the alarm time. That bit works fine too. Thirdly, alarm clocks never wake me up, so I'm building a digital sensor into my bed that will prevent the alarm from being turned off if I'm in bed. I can read the value of this sensor no worries.

So here's the problem, I want to set up a statement that will turn the alarm on if a)I'm in bed and b)the actual time is the same as the alarm time.

This is the statement as it stands, but it doesn't work. alarm_off is a digital input, I have tried using both ==1 and ==HIGH, neither work.

if( time_h == alarm_h   &&   time_m == alarm_m && alarm_off == HIGH) 
    digitalWrite(LED, HIGH);
    Serial.print("alarm on");

If I use this code the LED comes on, and the message is printed to the terminal:
if( time_h == alarm_h   &&   time_m == alarm_m )
    digitalWrite(LED, HIGH);
    Serial.print("alarm on");

Basically, the second of the two statements works perfectly, but as soon as I add a third condition, it doesn't.

Any ideas? I'm wondering if there's a limit to two conditions or something like that.
14  Topics / Science and Measurement / Re: Brewing thermostat on: July 04, 2011, 07:36:43 am
Problem solved, it turns out the 7805 I had was interfering with the LCD in some way, I'm not entirely sure how, but I've gotten rid of it and it works fine. Does anyone have any ideas why this may have been a problem?
15  Topics / Science and Measurement / Re: Brewing thermostat on: July 03, 2011, 06:33:01 pm
Hmm, good point.

The farthest into double checking that I've been ale to get is the display half of the circuit. I've checked so many times that the RS, EN, and D4-7 pins are connected to the right pins, and they are. For some reason though, when I power the circuit up, I get the first row filled with the black rectangles that make up the characters' spots, and the second row is empty. At the moment, getting the display working is the first priority, because the rest relies on it, and the rest is much easier to test/fix.

I'll see if I can come up with some good photos, but does that problem scream out to anyone as being caused by a particular thing?
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