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Location:
1st street on the right
Registered:
November 2002
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Who can help with building a temp gauge?
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Tue, 03 May 2005 04:55
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I know there's lots of elec guru's out there. Incl River who I'm sure will tell me to desing something using a PET.
Need to run a LCD display of temperature in a room and in a compressor cabinet. Display will be in a shop front, the senders will be approx 40 meters way. Cabling isn't a problem but what senders should be run and what LCD should be run to work with them? Also how do I go about making the LCD display from the senders signal?
thanks in advance
J
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Location:
Adelaide
Registered:
September 2003
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Re: Who can help with building a temp gauge?
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Tue, 03 May 2005 10:35
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I dont know myself but try calling a large Data Coms or Electrical company. Ask specifically for someone who is an expert in BMS.
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Location:
Pine Rivers QLD
Registered:
April 2005
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I Supported Toymods
Location:
Sydney
Registered:
December 2002
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 04:34
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Unfortunately thermistors are not a linear device so if you modify an already built product by extending the cable you might have cause a 3 degree temperature difference at one temperature extreme but could have 20deg temp difference at the other.
If you hack apart the unit you might be able to wire up the LCD display section via ribbon cable.
So long as the voltage drop is small enough that the display powers up you will not have altered the accuracy of the thing.
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Location:
1st street on the right
Registered:
November 2002
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 09:13
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Thanks for the replies. Had a quick browse of the links but my knowledge of elec's is limited to 12v on 4 wheels. I understand the problem of voltage and signal loss over distance. Was hoping to run a signal over Cat5 cable as the rooms are already connected with a spare line.
More in depth I'm running a compressor in a room outside the shop. I want to run a led to show on/off status, using 1 pair & 2 x temperature signals using 2 x pairs, if thats all I'll need. One temp in room and other temp in compressor cabinet.
The compressor is 3 phase with control circuits of 24V A/C. Am hoping to use this to power the stuff if possible.
Have seen the Jaycar units but am unsure about hacking and re-soldering the wiring and the effects it will have on signal (would need a second unit to check accuracy) and since it needs to be read by people who would be less than knowledgeable about what they are looking at...
EnFlaMeD: What is a BMS?
ndgcpr: What is SMD? Was looking to use LCD for numerical readout reater than leds.
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 10:38
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Hey hey hows its going mate.
I'll get around to doing that other project of yours as soon as I get some time to scratch my arse.
I'll also do this one for you as well as its simple as pie. A simple LCD, a PIC and a Dallas temp sensor is all it takes.
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Location:
Brisbane
Registered:
May 2002
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 11:15
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| clubagreenie wrote on Wed, 04 May 2005 19:13 |
ndgcpr: What is SMD? Was looking to use LCD for numerical readout reater than leds.
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SMD = Surface Mount Development I believe. If you have ever taken the cover off your phone or similar thats what it looks like, except a little bigger (phone stuff is usually smaller than what you would have to deal with tho!).
You could look at using something like a LM135?? With an opamp (gain), and a dc offset to cal it and then you could use a $10 Digital Multimeter (DMM) to display the result in mV or something (and have the reading on the DMM as deg C)?
lol, prbly not the most elegant solution?
But its an idea...
http://www1.jaycar.com.au/products_uploaded/LM135. pdf
Cheers
Wilbo
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Location:
Land of Oz
Registered:
June 2004
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 11:27
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Hi,
I saw this post but for some reason thought it was something to do with water temp gauge on your car.
What Cool1 said is the best bet. Check up info on the Dallas 1620 chip. It's a temp detection chip that sends data (9bit) that tells you the temp.
You hook this up to a simple microcontroller, such as the 16F84 or something similar to get the readings from the 1620 chip and to run your LCD display.
Here's a link on how to do something like you want using the Basic STAMP - which is a microcontroller that you can program in BASIC.
http://www.parallax.com/dl/docs/cols/nv/vol1/col/n v2.pdf#search='dallas%20temperature%20chip'
Failing that, I'm sure I can come up with some way to get the PET to get the temp and send it to you.
In any event, check out the Dallas 1620 chip to get some idea of what it is and how to connect it. Also I think Dallas Semiconductor have various applicaiton notes on their site that will provide info on how to use the chip.
Tell Cool1 to move his ass and get his other project out of the way so he can build/program it for you.
SMD is Surface Mounted Device. They're really small and the pins on the chip are very close together. They're designed to sit in the surface of the circuit board, as opposed to the older DIL style where the pins went into holes on the cct board. Unless you have the proper equipment, good eyes, magnifying glasses and a a very steady hand, it's best to keep away from these if possible - especially on the SMD devices which have a lot of pins.
BMS, to me, means Basic Mapping System, which is a method of doing realtime relocation of CICS program maps and code, usually via assembler (for speed and tight code) into virtual storage on IBM Mainframes. I used to write BMS code. I also wrote some of the Box Triffecta code for the NSW TAB. Next time you put your money on a Triffecta you can think of me!
seeyuzz
river
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Location:
Land of Oz
Registered:
June 2004
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 11:45
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Hi,
Just re-read the posts and Wilbos idea isn't a bad idea, but, like some of the other ideas presented, you'll have to tweak the cct (probably constantly) to allow for varying output of the temp sensor due to allow for temp variance. As the sensor circuit warms and cools it's output linearity will change and therefore change your final reading. The Dallas chip, I beleive, is self-compensating.
However, expanding on Wilbos idea, you purchase a cheap DMM (Digital Multimeter) that has a temp selection on it and just hook it up to your equipment or whatever. Remove the batteries from the DMM and connect it to a small plugpack to provide the power (saves you on batteries also). These DMMs aren't very expensive and Jaycar has some in theie catalog. They're pretty accurate and you just gotta make sure you get one that doesn't have an auto-cutoff so it will stay on all the time. In any event, there's ways of getting around the auto-cutoff and provide a small timed-switching circuit with a 555 and a few components. Getting smarter you can also have a couple of inputs and switch them so the DMM reads the temp of equipment-A for a few secs, then the input is switched so it reads equipment-B for a few secs, and then back to A and so on.
If you need something that alerts you when the temp exceeds a certain limit, then you're better of with the 1620/microcontroller solution.
seeyuzz
river
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Location:
1st street on the right
Registered:
November 2002
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 12:46
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OK. So I'll need a 16F84 and someone to program it. A 1620 to sens temp and someone to show me how to build it.
River, the 1620 is a better solution as I'll probably want to upgrade it's functions to include controlling the compressor at high temp. The display ideally would show both temps at the same time, so would I need 2 of everything or just 2 1620's?
Would the controller need to be located with the 1620? If so how many wires are needed to connect to the LCD? I should have 2 pairs in a CAT5 line to use, another if necessary but were planned for something else. Am using the cat as I don't need to run conduit for it through the building.
Or can I locate the controller near the LCD and need less connection between the 1620 and the controller?
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Location:
Land of Oz
Registered:
June 2004
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Re: Who can help with building a temp gauge?
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Wed, 04 May 2005 22:44
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Hi,
You'll need two 1620 chips - 0ne for the compressor cabinet and one for the room. They communicate to your microcontroller via a 3-wire interface.
The 1620 also has low and high temp threshold outputs. You program the 1620 to specify your lower/upper temp limits. When these limits are met it outputs a signal on the low or upper threshold line. Therefore, it is possible to use the 1620 as a thermostat and, by using its upper/lower output lines it can switch on or off devices as the temp thresholds are met. However, this doesn't provide you with a display.
So, if you want to display the temp then you'll need the microcontroller/LCD setup. Your microcontroller will constantly read the temp registers of the 1620 and display them. I assume that you must have some upper/lower temp limits for your situation? When these limits are met you want the m/c to switch off (or on) the compressor.
Are your temp limits static or do you want to be able to configure the temp thresholds as you desire. If you want static limits then you don't really need a keyboard, if you want to change these limits then you'll need a keypad or a couple of buttons. Do you want a buzzer or some other device to sound an alert that a temp threshold has been exceeded?
You'll need 4 (or is it 5? - I'll have to check) lines minimum to control the LCD, assuming you use a parallel LCD. You can use a serial LCD to reduce the number of lines required, but these are more expensive.
So, basically - assuming static temp thresholds - you'll need 6 lines for the two 1620 chips (3 lines per device) and 4/5 lines for the LCD display. You may be able to get away with less than 6 lines for the two 1620 devices by using some multiplexing, assuming this doesn't upset the 1620 chips.
If you want to turn something on or off, then you'll need a line for each one of these. If you want a manual override to turn things off/on, then you'll need a line for each override button. An audible threshold buzzer would require a line also.
The number of lines required may exceed the number of lines the 16F84 has, so you may have to go to the next level m/c chip - which isn't a big issue.
The 1620 chips can be remote. I don't think there's a lot of loss through Cat-5 and it may be okay. I assume we're not talking about a huge distance involved. You'll need to provide power for the 1620 devices. This can be through the Cat-5 or by a plugpack at each location. If using the plugpack, make sure the earth wire is connected to the m/c to ensure no floating earth and to stop other spurious readings and spikes.
You need to specify what functions you want - ie, audible alert, manual overide, ability to change temp thresholds, relay control to turn comp off/on, etc. Using this info we can then derive the number of lines your m/c will need to have.
Sorry to be so long winded. I just can't help myself.
seeyuzz
river
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: Who can help with building a temp gauge?
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Thu, 05 May 2005 01:49
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i am sorry but i haven't read every post in great detail so it may have already been mentioned. I was cruising the net and found this (i think it may ba alittle like the dallas one)
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2025 .
it sends frequency not voltage so voltage drop isn't a prob. it will save worring about the A/D converters too.
Oh and if you want LCD stuff i find this site helpful
http://home.iae.nl/users/pouweha/lcd/lcd.shtml
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