Has anyone made their own thermometer circuit?

I am trying to work out the details of my new rig. I have built a PWM circuit to control my BK temps. Now I need to figure out a good solution for monitoring temp in the BK and MLT. I would like to panel mount a digital display to read the temps. Most of the panel mounts I have found are more expensive then a PID. A PID seems overkill for just reading temp.

My other thought was to buy a couple of Digital thermometers from wally world and tear them apart and mount the LCD on my panel. Then I thought I could just make one.

Any thoughts on this? I have not found a good schematic yet so I am a bit hesitant.

I was looking once to make a small heater for inside my fermentation chamber for use when it was colder in the garage than my Ale wanted to be. I'm am electrical engineer with a big sack of random electronics parts laying around, so I thought I would just cobble a little thermostat together and use it to kick on a lamp.

Unfortunately, what I would was that the price of a thermistor was way higher than I had expected and it ended up being much cheaper (not to mention easier) for me to just buy a cheap-o thermostat at Lowes and use that.

So, while you could definitely build your own little circuit, you would likely not be able to match the price of a WalMart digital thermometer off the shelf.

OUt of curiosity, I did another search and found that you can get a temp sensor for $8. This is SIGNIFICANTLY cheaper than what I had found during my search a couple of years ago.

http://www.omega.com/ppt/pptsc.asp?ref=AD590&ttID=AD590&Nav=

Now, if you want a digital read-out of the temp, you need to buy or build an analog-to-digital converter, which is going to cost a bit more.

Originally posted by SAWDUSTY

http://cgi.ebay.com/New-LED-RED-Dig...emQQptZLH_DefaultDomain_0?hash=item3ca7212d35

Cheers,
ClaudiusB

Brewmoor said:

I am trying to work out the details of my new rig. I have built a PWM circuit to control my BK temps. Now I need to figure out a good solution for monitoring temp in the BK and MLT. I would like to panel mount a digital display to read the temps. Most of the panel mounts I have found are more expensive then a PID. A PID seems overkill for just reading temp.

My other thought was to buy a couple of Digital thermometers from wally world and tear them apart and mount the LCD on my panel. Then I thought I could just make one.

Any thoughts on this? I have not found a good schematic yet so I am a bit hesitant.

Click to expand...

Build one from a Kit. This Digital Thermometer Kit is $22.92 and uses an LM35 as a sensor. It would look mighty nice mounted in a panel. It beats ripping a Wally World digital thermometer apart. For the probe, simply solder some wires to the LM35 and insulate them with some heatshrink sleeving, smear some thermal heatsink goo around the LM35 and slip it into a thermo well.

Sawdustguy said:

Build one from a Kit. This Digital Thermometer Kit is $22.92 and uses an LM35 as a sensor. It would look mighty nice mounted in a panel. It beats ripping a Wally World digital thermometer apart. For the probe, simply solder some wires to the LM35 and insulate them with some heatshrink sleeving, smear some thermal heatsink goo around the LM35 and slip it into a thermo well.

Click to expand...

This might be the way to go. I am going to denver this weekend. I will check tjmax and their home store for super cheap digitals. If I don't find anything cheaper I think I will build that.

I think the LM35 is Celsius. There is a direct replacement if I remember right for F.

Edit: That kit is cutting it close. The operating range is up to 99C that is about 210F

Ok I think I have found the solution. Semi DIY

This Digital Thermometer or one similar.
Walmart

Bonus it has a timer on it for keeping track of hop additions. I am already using a computer power supply to power my circuit for the boil kettle control. So....

I am going to use a 5v leg on the power supply to power the thermometers so I don't have to keep feeding them batteries. I figure I can use this simple circuit to get the voltage down to 1.5v ......the same a AAA battery.

Brewmoor said:

I think the LM35 is Celsius. There is a direct replacement if I remember right for F.

Edit: That kit is cutting it close. The operating range is up to 99C that is about 210F

Click to expand...

LM34 is the F version. If you use a real long probe, pay attention to what the datasheet says about capacitive loads.

Both are actually rated to about 300 F (150 C), it's the circuitry in that kit limiting it, maybe for more accuracy in the intended range.

goose_on_fire said:

LM34 is the F version. If you use a real long probe, pay attention to what the datasheet says about capacitive loads.

Both are actually rated to about 300 F (150 C), it's the circuitry in that kit limiting it, maybe for more accuracy in the intended range.

Click to expand...

Either that or they were too cheap to throw another 7 segement LED on there to give you the "hundreds" digit.

Ok....Here is what I came up with.

I found a 12v power supply from an old router. It will power my PWM circuit for the boil kettle and two thermometers. One to monitor the MLT and the other for the BK. The HLT will be monitored and controlled from a PID

I got two Taylor digital thermometers from Target. About $15 each.

They use a AAA battery, 1.5v. So I needed a circuit to cut the power from 12v to 1.5v. Here is the circuit I used



Here are the results. The thermometer seems to be working fine. I think this might work.

how how is the 317 getting on you?

Walker-san said:

how how is the 317 getting on you?

Click to expand...

Not sure what you mean.

Brewmoor said:

Ok I think I have found the solution. Semi DIY

This Digital Thermometer or one similar.
Walmart

Bonus it has a timer on it for keeping track of hop additions. I am already using a computer power supply to power my circuit for the boil kettle control. So....

I am going to use a 5v leg on the power supply to power the thermometers so I don't have to keep feeding them batteries. I figure I can use this simple circuit to get the voltage down to 1.5v ......the same a AAA battery.

Click to expand...

Don't forget to use a 1/2 watt resistor. You should be dissipating about 300mW if my guestimate of current draw is correct.

i used the lm317 with a stirplate i built...don't you need a heat sink with that?

I did some kind of overkill thermometer with a pic, i2c sensors D1820, and i2c 4 digits 7 segments display with SAA1064.
Worked well, but was a base for a full temp control of my setup.
Project has been killed by my first child and now I got a new 6 weeks old baby, I ain't got time to work on this project.
It will wait a bit more and I brew "good ol time" way

Sawdustguy said:

Don't forget to use a 1/2 watt resistor. You should be dissipating about 300mW if my guestimate of current draw is correct.

Click to expand...

Yeah I scrapped that idea. I did not have the right size zener diode. I did have a voltage regulator so I went with that circuit instead. I did use 1/2watt resistors on that circuit.

scinerd3000 said:

i used the lm317 with a stirplate i built...don't you need a heat sink with that?

Click to expand...

I put one on it but it seems like it is not drawing very much power. It is stone cold. Maybe when I add the second thermometer it might get a little warm.

Brewmoor said:

I put one on it but it seems like it is not drawing very much power. It is stone cold. Maybe when I add the second thermometer it might get a little warm.

Click to expand...

Maybe I am confused, but the 317 is what you have that big heat sink attached to in the picture, isn't it? That's why I asked how hot it was getting.

Arduino is a great option for projects like this. You may have to learn some code and logic/programming techniques, but it's a very powerful microprocessor. There is example code all over the internet. You can display up to six LM34/35 inputs on a serial LCD, and if you get a bit more sophisticated, you can even use it to control the temperature using solid state relays and/or transistors.

Walker-san said:

Maybe I am confused, but the 317 is what you have that big heat sink attached to in the picture, isn't it? That's why I asked how hot it was getting.

Click to expand...

Ah you mispelled hot. "how how". I was a bit confused. It is not getting hot at all. It was cold to the touch after about ten minutes on. It is a very small load.

Yuri_Rage said:

Arduino is a great option for projects like this. You may have to learn some code and logic/programming techniques, but it's a very powerful microprocessor. There is example code all over the internet. You can display up to six LM34/35 inputs on a serial LCD, and if you get a bit more sophisticated, you can even use it to control the temperature using solid state relays and/or transistors.

Click to expand...

That might be an upgrade I do later. I have been looking at those boards on Make.com. I am not all that good at programming. though I might start looking into more this winter. I just want to get my rig brewing first.

ha- somehow i missed the giant heat sink in the picture...sorry