# Very inexperienced looking for help **URL:** \ **Category:** Projects\ **Created:** [September 24, 2014, 5:51am UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475 "2014-09-24T05:51:22Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![MCSteven](https://avatars.discourse-cdn.com/v4/letter/m/c37758/32.png) [@MCSteven](https://community.sparkfun.com/u/MCSteven)\ **Post date:** [September 24, 2014, 5:51am UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/1 "2014-09-24T05:51:22Z")
Thanks for reading and helping if you can. I would like to build a device that compares two temperatures (one being the room temp and the other being the air coming from the HVAC vent). I would like the device/circuit to produce a powered output one way or the other. If the temp is the same or colder from the vent, it can be +, or off, or anything else. If it senses that the vent is producing high temp, it would be a -, or on, etc. While I’d be ok with just the two states, if the cost, effort and labor is minimal, a three state (hotter, colder, relatively close to same temp) could also be used. If this is something to be built what would you charge to build it. I currently do not have tools or space to build. This is my first post and I can see myself returning often. 😃 Thanks, MCS ---
**Author:** ![Ross\_Robotics](https://avatars.discourse-cdn.com/v4/letter/r/cc9497/32.png) [@Ross\_Robotics](https://community.sparkfun.com/u/Ross_Robotics)\ **Post date:** [September 24, 2014, 4:21pm UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/2 "2014-09-24T16:21:42Z")
Check your PM. ---
**Author:** ![lyndon](https://avatars.discourse-cdn.com/v4/letter/l/7993a0/32.png) [@lyndon](https://community.sparkfun.com/u/lyndon)\ **Post date:** [September 24, 2014, 6:23pm UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/3 "2014-09-24T18:23:51Z")
What you are looking for is called a [[differential thermostat](http://www.ledclocks.com/controllers/DSD2DifferThermostat.html). How many do you need built?]([Differential Thermostat DSD-4](http://www.ledclocks.com/controllers/DSD2DifferThermostat.html)) ---
**Author:** ![MCSteven](https://avatars.discourse-cdn.com/v4/letter/m/c37758/32.png) [@MCSteven](https://community.sparkfun.com/u/MCSteven)\ **Post date:** [September 25, 2014, 6:05am UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/4 "2014-09-25T06:05:17Z")
Thank you both for replying. My imagination my have overpowered my budget. I looked at a number of commercial ones or stuff from small manufacturers. Even the smallest seemed to be $30 a piece and did more than I needed. I simply need to have a different output if one measurement is hotter than the other measurement. As mentioned, it can be off until it’s hotter, then it send a signal. This is for a simple 12V (or 5V) project. ---
**Author:** ![Ross\_Robotics](https://avatars.discourse-cdn.com/v4/letter/r/cc9497/32.png) [@Ross\_Robotics](https://community.sparkfun.com/u/Ross_Robotics)\ **Post date:** [September 25, 2014, 6:10am UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/5 "2014-09-25T06:10:06Z")
It’s going to cost more than $30 for parts, much less the labor involved for designing it and assembly. ---
**Author:** ![lyndon](https://avatars.discourse-cdn.com/v4/letter/l/7993a0/32.png) [@lyndon](https://community.sparkfun.com/u/lyndon)\ **Post date:** [September 25, 2014, 12:16pm UTC](https://community.sparkfun.com/t/very-inexperienced-looking-for-help/29475/6 "2014-09-25T12:16:39Z")
It can be built for less than $30 in parts, but you’d definitely have to DIY. I have a design somewhere that does this. It was for an attic vent fan that turned on if the attic was x degrees hotter than the outside air. Parts probably cost around $10. You could build it on a kitchen table. But as you (codlink) say, having someone do it for you will certainly cost more than $30 assuming you want them to do a good job.