Elk M1 Humidity Sensor?


Active Member
Hey Cocooners,

Wondering if anyone is monitoring the humidity in their home via an Elk panel? Since it could use an analog sensor I wondered if anyone was doing that, and with what/which sensor.

In the past I think a few people suggested a 1-wire option but I don't believe that to be the easiest route (since you need to run a 1-wire "hub" somewhere?) and needed some software.

I'm thinking about just a plain variable voltage output sensor I can plug right into a Elk zone and write some rules around it.

I monitor the light levels in my home using analog CDS sensors, so the monitoring part will be easy. However, as far as I know, you can't trigger rules when you hit a certain value, since the voltage level has to be polled. So you would probably require a PC to do the polling & processing (which is what I do).

If you find a cheap humidity sensor, please post here.
The Elk will do the polling for you.

Create a rule similar to:
Every minute
and test analog level
then ...

You cannot trigger a rule strictly based upong the analog level changing, but "every minute" is usually quick enough. I think you can shorten then to every few seconds if you really need it without any performance hit, there was a discussion about this on the Elk message board.
I already tested the Every 1 Minute rule that WayneW says with a CDS sensor. Its very easy. Make sure that you use the Status button in the Elk-RP toolbar to see the actual analog value of the input zone. In this way you will be able to know what value you should use to trigger your rule (together with the polling time).

Values range from 0 (zero resistance) to 13.8 (very high resistance). The EOL of 2200 give you aroung 7 volts. One warning. I noticed that Elk-Rp would give an Overflow Error ancd closes abrubtely whenever the comparison value was close to 13.8.
elcano said:
Values range from 0 (zero resistance) to 13.8 (very high resistance). The EOL of 2200 give you aroung 7 volts. One warning. I noticed that Elk-Rp would give an Overflow Error ancd closes abrubtely whenever the comparison value was close to 13.8.
Yep, that's the whole purpose of the EOL. If you have a variable voltage input on a zone set for say a typical door contact application and vary the voltage in, you would see that zone fault until the voltage in was around five or so volts. Then when the voltage got past seven or so volts it would fault again.

Thus when the EOL resistor is installed near the sensor, nobody can cut through your wall and "short out" this zone and bypass that alarm.
If you are looking for the actual sensor, you can probably use something like a Honeywell HIH-3610. It's a small 3-pin device that requires power (nominal 5v) and returns a variable voltage based on humidity.

There are other types of sensors out there that vary capacitance with humidity but you need to add additional circuitry to use them (typically a 555 timer to convert capacitance to frequency and more stuff to convert frequency to voltage).

Newark carries them: HIH-3610 at www.newark.com. There are other models and variations.

Here's the manufacturer's page: Honeywell HIH-3610.

I have used older versions of these in the past in a 1-wire setup by using a DS2438 as an A/D converter. But, for the Elk you should be able to use the voltage directly.

I do not know how long a wire run you can use, however. Note that they are also light sensitive so you should hide them in a box or something.

Here's another thread mentioning the sensor: CocoonTech: Humidity Sensors?. I'm sure these have been discussed here in other threads but I can't find them (maybe it's on the HS board?).
As I said in the other thread that smee mentions, I'm using a Honeywell HIH-3605 in a project. I'm reading its output using a ADC0831 A/D chip, which has 8 bit resolution over a scale that you can set with a reference voltage. I use a 4.3 volt zener diode to get a 256 step scale from 0 to 4.3 volts. This is to get a 1 to 1 relation between a 1% change in humidity and a two bit change in the A/D converter's scale (ie: the HIH-3605's output changes by 32 mV per 1% RH change and the A/D resolves to 1 bit for every 16 mV. It then becomes a simple matter to subtract the zero offset and divide the value by 2 to get a straight %RH value.

I don't know what voltage scale the Elk's A/D range is spread out over, but I think I've seen someone mention 14 volts in a past discussion. In a case like that, you would get a roughly 3% RH resolution, which is still good.
The A to D input range is 0 to 13.8 volts with an eight bit resolution or 256 steps. You can go to menu 8 on the user menu and watch the A to D values and calculated zone voltage as you change the input voltage to a zone.

Had several requests for water sensors to the M1. George Risk Industries makes a simple water sensor for screw to a wall mount or under carpet mount. You can also just take two stainless steel probes and do the same thing. If you take two conductors of wire to a zone input and dip the two conductors into a glass of water (slightly dirty is better) it will pull the zone input to ground, violating the zone.

Happy M1ing!