Is there a way I can build or buy a device to send and receive a 5v transducer signal wirelessly about 1km. It is a variable dc voltage up to 5v depending on reading. The transmitter needs to be simple reliable and inexpensive.

 

http://wonderfulengineering.com/10-best-rf-modules-for-arduino/

1km is pushing the limit for simple electronics, but still doable. Link above is for Arduino modules.

 

To get the maximum range you could add an RF coax cable to the ones that have detachable antennas and mount the antennas outside on the roof.

 

Depending on the available power supply, an ESP8266 might be a good selection and link back to a WiFi network.
It could also be a good use for a LoRa system if there is a network nearby. Or you want to set your own up.
Many ways to skin this cat. What is your required data rate and how your budget, in $ and in power.
And is this a one off or will there be a few?

 

I think you could achieve your 1 Km range (LINE OF SIGHT. I.E No trees or buildings blocking the path.) using HC-12 modules. These work at around 433 Mhz. You may need to use directional antennas. As this is in the amateur radio 70cm band you should be buy them ready made. I have used HC-12s for this sort of remote data monitoring but not over such a long range. One of the sensors I have built just uses a PIC12F1840 and an HC-12 for the transmitting end. The ADC in the PIC reads the voltage and the PIC then converts the data to a text string which can be read using a PC or tablet connected to the receiving HC-12 running terminal emulator software. I can also use a Raspberry Pi at the receiving end to lig the data to a file.

Les.

 

An esp8266 module with a good antenna will work, if you are to believe these very credible tests (see video below).

I would add that you can try to use a second esp8266 module as a receiver. That is, no router is needed - I do that all the time. Don't know what distances would be available in that configuration, and, again, the appropriate antennas on both ends would be a consideration.

 

I've seen reports of 20-30 miles line of sight wifi with directional antennas so that video is believable.