I have been slowly converting all of my HSM100, Everspring SM103-1 Door/Window Sensor and ST812-2 Water/Flood Sensors to external power. I picked up a bunch of 5v DC transformers only to find out that the actual voltage ranged from 7 to 11.5 even under a small load. This voltage tolerance would inevitably cause my devices to fail plus fluctuating line voltage would increase that risk. Depending on the device I need either 5v (3 AA batteries) or 6v (4 AAA batteries) I started a project to create a simple and cheap solution. The goal was to regulate the source voltage while using a variety of DC transformers with output voltages up to 18v.
I have a solution that has been running flawlessly for over four months now and it cost me $0.40 plus the power supply. I thought I would share it with those who are not afraid to dissect their devices. If you decide to try this solution for yourself remember you do so at your own risk.
What you need:
DC transformer up to 18v. (5V min to 18V max)
Fairchild Semiconductor LM7805CT Voltage Regulator in a TO-220-3 case for devices needing 5v
or
LM7806CT Voltage Regulator for devices needing 6v
I have attached pictures showing my simple construction on the HSM100 but the process is very similar for other devices. Remember that the heat sink on the LM7805CT or LM7806CT is connected to ground so cover it with electrical tape or heat shrink tubing.
After soldering the wires onto the regulator leads I used small heat shrink tubing to cover them, make sure you put the tubing on the wire(s) before soldering the wires.
A stable voltage supply usually makes for a reliable device even in extreme temperature conditions.
It might or might not matter in a particular instance, but the data sheets for these voltage regulators also specify a capacitor across both the inputs and outputs.
The two capacitors are used as hi-pass and low-pass filters. (these filter power line noise) If you look at the picture of the circuit board you will see to the right of where the positive wire is soldered there is a low-pass capacitor going to ground there. In most power supplies the hi-pass filter is included so neither capacitor is needed.
Thanks for the info, I was just starting to look into doing this! It’s amazing how they can even sell transformers that vary that greatly. I always assumed that “Wall Warts” were more stable than that. I guess buy saving a few pennies they make more money and we get an unreliable DC feed that we then have to stabilize the power to what it should be.
Your post saved me hours of troubleshooting, or worse yet, a fried HSM100. Those are not exactly throw away modules that’s for sure.
Glad to share this with you. I initially started this project because I had a whole drawer full of power supplies with a wide variety of output voltages that had no use in my z-wave system. Now I can use any of them that are less than 18v. I found it a great way of recycling junk.
I have a few HSM100 mounted outside and another two inside all powered from one power supply located in my electrical room. The LM7805CT Voltage Regulator can handle up to 1 amp so as long as you have a 1 amp Wall Wart you can share the power.
Yes you could use the power from the PIR. That voltage is usually between 4.5v to 14.5v. Obviously if it is 4.5v your good to go otherwise you can use the voltage regulator to reduce it. Keep in mind that you will need to add the power the HSM100 is using into the power calculation for the alarm system. As an alternative many alarm systems are wired using 3 pair wiring. The PIR uses one pair for power and one for the trigger leaving one pair free. You could find that pair and use it to power your device.
[quote=“JimMac, post:7, topic:170269”]Glad to share this with you. I initially started this project because I had a whole drawer full of power supplied with a wide variety of output voltages that had no use in my z-wave system. Now I can use any of them that are less than 18v. I found it a great way of recycling junk.
I have a few HSM100 mounted outside and another two inside all powered from one power supply located in my electrical room. The LM7805CT Voltage Regulator can handle up to 1 amp so as long as you have a 1 amp Wall Wart you can share the power.[/quote]
@JimMac
Can you post a photo of this power distribution? I wasn’t sure this was possible, and it’s ideal as I have security wires running all over the place and wanted to tap these to run my hsm100s since they come back to a central area, but plugging a bunch of wall warts in and splicing the wires into each one for each sensor didn’t seem right… Your direction on this is appreciated!
This voltage regulator is rated to deliver up to 1 amp “with adequate heat sinking”. How much heat sinking needed will be dependant on the current drawn and how much it is dropping the source voltage. These sensors draw very little power, so there should be no problem with heat in this application.
@big517
I’m not at my lake house to get any photos but there is nothing to it, just a little leg work.
If you want to use the 12v power from your alarm panel then wire up your HSM100 as per the instruction except replace the Wall Wart power supply with that from the PIR, smoke detector or other alarm devices. Connect a pair of wires to both the + and - on the alarm device and connect the + wire to pin 1 and the - to pin 2 of the LM7805CT.
Edit: Last weekend I modified my two HSM100 that are mounted outside, now they are being powered from a Q-See security camera close by (12v DC).
If you are looking at using any spare wires from your alarm panel first make sure the cables used in your system are 3 pair or more (some smoke detectors use all three pairs). The best way is to cut back the insulating jacket a half inch on the cable you want to use. Unused wires will be either cut off or wrapped around the jacket depending on who installed the cabling. If you do find some, check the other end of the cable just to verify they are not connected to anything, sometimes unused pairs are wired to a spare connector on the terminating block of the sensor. Use a multi-meter for testing just to be safe. If you find a pair that can be used then wire up a wall wart with the regulator as per the instructions and connect the + and - outputs to the spare pair. At the alarm sensor end extend that unused pair to your HSM100 and connect the wires to the HSM100 circuit board as shown in the instructions above. Make sure the polarity is correct prior to applying the power. It may not be necessary but during my testing I attached a small isolated heat sink to my LM7805CT. Even powering 4 HSM100 I have never felt any heat from it.
As usual the standard disclaimer applies, I accept no responsibility for any damage you may cause to your equipment, yourself, your neighbors, pets…
Jim, how are the HSM100s holding up exposed to the elements? Did you do anything special to protect them?
I’m still waiting for the Aeon outdoor sensor, so I can get outside temp and light readings, but I am no longer holding my breath on that one :). Thinking of just sticking an HSM100 under an overhang…
How did you seal them? I was thinking about silicone and making them airtight… What did you use, what type of conditions are they exposed to, and how long have they been exposed?
Thanks for this. I added this to 2 of my HRDS1 door sensors this weekend. It was simple, and the output voltage is a constant 4.9 v with several 5 to 7.5 v wall warts. Radio Shack carries this in-store for $1.99, Model: 7805 | Catalog #: 276-1770.
I have 4 HRDS1s that I’ve used for a year plus 2 new in box I haven’t installed yet. 3 had been running on wall warts (without voltage reg) pretty reliably, but one had stopped responding with LED indications, even when I switched back to batteries. I assume it got too much voltage. But I may give it another shot to try to re-add it.
Another one of these exhibits a strange behavior. It is on a wall wart, and for several minutes after power up will act normally with LED activity when tampered or switched. After a period of time, triggering it does NOT make the LED light up, but it still seems to be triggering vera! So maybe my ‘bad’ one is still working, just not lighting up. I’ll give it a try soon.
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