secu16 +temperature sensor

jduncc

Member
I'm looking to add two temperature sensors to my secu16, one to monitor temperature in a fridge in the garage and a 2nd to monitor temperature in the attic. The bobcats seem a little pricey, and I noticed some people use the lm34. I'm looking for a little guidance for connecting a lm34 to my secu16.

LM34 from Jameco

Looks like I need to create a little circuit that actually connects to the secu16. I don't have my ocelot and secu16 hooked up yet, but do I need to get a power supply for the secu16? In addition to the temperature sensors, I plan to monitor the two garage doors using the magnetic contacts, as well as the 3 exterior doors to the house.

Thanks!
 

BraveSirRobbin

Moderator
You can actually set-up the SECU16 to establish an on or off based on analog input setpoints. I'm not sure how to do this as I don't have an SECU16, but you can look at its manual HERE.

You do know that the link you provided was for a "surface mount" chip (meant to be mounted on a PC board).

You may want to look into a TO-46 or TO-92 package for that unit as it will be a little easier to mount on a breadboard setup.

Also, you should be able to "daisy chain" the power supply from the Ocelot to the SECU16.
 

jduncc

Member
So does that mean I can put the LM34 on a breadboard, then wire the breadboard directly to my secu16? I don't need to wire in any resistors or anything?
 

BraveSirRobbin

Moderator
No I didn't say that. I was just pointing out that the surface mount would be harder to work with. I believe the schematic did required resistors that you calculate based on the desired range/output.

I never used one, so I don't know any more details.
 

Guy Lavoie

Active Member
jduncc said:
So does that mean I can put the LM34 on a breadboard, then wire the breadboard directly to my secu16? I don't need to wire in any resistors or anything?
As BSR pointed out, you are better off getting the TO-92 style case for your LM34's. You can share the same power supply for your Ocelot and SECU16, but you will need a seperate power supply for the LM34. This can be either a 5 or 12 volt supply but it needs to be well filtered and regulated. Another question is: will you need to measure temperatures below zero? This can be done but requires a different method in connecting and powering the LM34, and a bit of math in C-Max to deal with the offset now created due to shifting of the output voltage range. Finally, the analog resolution of a SECU16 input means that you will get a 2 deg F resolution; is that close enough for what you want to do?
 

jduncc

Member
Guy Lavoie said:
jduncc said:
So does that mean I can put the LM34 on a breadboard, then wire the breadboard directly to my secu16? I don't need to wire in any resistors or anything?
As BSR pointed out, you are better off getting the TO-92 style case for your LM34's. You can share the same power supply for your Ocelot and SECU16, but you will need a seperate power supply for the LM34. This can be either a 5 or 12 volt supply but it needs to be well filtered and regulated. Another question is: will you need to measure temperatures below zero? This can be done but requires a different method in connecting and powering the LM34, and a bit of math in C-Max to deal with the offset now created due to shifting of the output voltage range. Finally, the analog resolution of a SECU16 input means that you will get a 2 deg F resolution; is that close enough for what you want to do?
Guy - I am not sure what you mean by a regulated power supply. Would this 12v power supply from radio shack work? 12 Volt

In regards to resolution, I am assuming you mean that is how accurate it would be, yes 2 degrees is close enough. Now in terms of wiring, can you wire the LM34 directly to a cable that runs to the secu16 and the 12v power supply or do you actually need to build a little circuit for this? Can the 12v power supply power a couple lm34's?

Thanks for your help!
 

Guy Lavoie

Active Member
No that Radio Shack power supply is not regulated, it is just a simple "wall wart" that is designed to put out a voltage close to its rating at its maximum load. This model appears to be regulated:

supply.Regulated supply

Yes, this supply could power a whole bunch of LM34s without a problem. There is no need for an external circuit unless you want to build some type of amplifier to increase the resolution or something. All you really need to do is connect the 12 volt supply to the LM34's power and ground pin, and the LM34's signal out and ground pins to the SECU16's signal input and common respectively.
 

electron

Administrator
Staff member
what would be a good source for these LM34's? I have an Elk power distribution module, which can put out 12VDC, around 250mA per output, so this would be a cheap solution since I already have the power.
 

electron

Administrator
Staff member
Right, but BSR suggested another package, so wasn't sure if this was still the unit to go with.
 

electron

Administrator
Staff member
yep, went there, thanks! I just have to figure out which one to go with, since there is a big price difference depending on what temps you want to monitor.
 
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