Garage door sensor current draw

[Tim Streater]

Just did the measurements. Results:

Door partially open: 4.5mA Door ascending: 4.5mA Door descending: 30mA Door open and stopped: 4.5mA Door closed and stopped: 4.5mA

So it's clever enough not to bother sensing when ascending. The figure is not constant during descent, but it's a good enough number and doesn't affect any calculation given the low load factor of the descent stage. It also varies a bit in other phases.

This means that the cheapo AA have in fact a capacity of 750mAh or so, better than I expected. Anyone know what decent Energiser or Duracell might do?

[Spike]

Ultimate Lithium 3500 mAh, very flat discharge and temperature profile

Pack of 10 for £13:88:

[Tim Streater]

Thanks for that.

[Martin Brown]

That is a ridiculous amount of current for the thing to draw in standby. Anything more that 0.5mA standby is unacceptable for a long battery powered life (and 50uA is better still).

You should be able to find AA batteries with at least 2Ah real capacity. I have found Kodak cheapo 10 packs from Poundland about the best buy for don't care sacrificial use. They leak much less often than real Duracell which I now avoid like the plague in favour of Panasonic or Everyready.

[Paul]

The spec for the device:

******* Frequency Multifrequency system auto-adjustable 868 MHz

Standby / Operating consumption 0,1 mA / 12mA <===

Radiated power < 1mW Range (in open field) 50m Battery life (approx.) See battery life table

*******

So it's supposed to sleep at 100 microamps.

Has something been substituted for the correct item ?

Maybe the receiver on the item is constantly receiving an 868MHz signal and "waking up". The higher consumption figure would be while it is running the sensor and TX radio at the same time, that low figure is the micro waking constantly checking for messages on RX.

I wonder what would make an effective Faraday cage for a test (to try to get it to drop to 0.1 milliamp) ?

*****************************************************

Sounds like a good excuse to own an SDR. Now, this isn't working the door sensor, this is the decoding of the fob to open the door. As long as the RTL (RealTek) SDR has the frequency range for the carrier, you can at least use it for activity detection.

The frequency range of an RTL-SDR is nominally 24 ? 1766 MHz.

Version 3 with new features: HF direct sampling mode

Example of an antenna kit. I don't know exactly how this setup is impedance matched (the antenna is 300 ohms, the dongle input is 75 ohms). Normally you'd use a balun to go from balanced to unbalanced. I have all of the kit for this already, used for my OTA TV reception :-)

75 ohms on input, mentioned here.

The direct sampling mode adds 500KHz to 24MHz, which means in total, the device covers 500KHz to 1766MHz.

HF Direct Sampling Mode - Listen to 500 kHz - 24 MHz with direct sampling.

Anyway, the 1766 MHz synthesizer range, means 868 UHF would be receivable.

You can't always receive/decode just any arbitrary signal. The frequency hopping of Bluetooth would be a bitch to follow, especially if the hops go outside the sampling bandwidth of the thing. Not every modulation pattern is compact enough for GNU Radio to have a decoder for it. It's a miracle the silicon on what is essentially a DVB-T receiver, can be used for this "general purpose radio reception". The wide range front ends make this possible (RF synth operates well outside TV range).

Wifi at 2.4GHz and 5GHz, is also above the 1766MHz limit. And finding a 6GHz SDR because you wanted to listen to Wifi, is a significant adder to the pricing. So while it's fun to pretend, this isn't the "perfect" toy. At one time an RTL SDR was about £20, and there might be cheaper versions out there (maybe with a less-good crystal or something). So if you want to experiment with listening in to key fob data patterns (the unencrypted ones), this could be a fun toy for such things.

It helps if you have SDR software that is pre-configured for various tasks. Nobody wants to build a filter chain themselves particularly.

Paul

[Harry Bloomfield, Esq.,]

Tim Streater a écrit :

That is more than I would accept as a continuous load for a batteries powered item.

[Tim Streater]

I'm going to check these figures and then see what the garage door vendor has to say.

[The Natural Philosopher]

I thought it was supposed to be 100µA when the door was not operating???

I think its faulty

[Martin Brown]

That is more like it. Odd that every measurement is higher than the spec. You would expect peak consumption to be the same even if baseline was high if for whatever reason the thing wasn't sleeping properly.

Rover Assorted old style biscuit tin or an old paint tin with a 1/4" mesh lid on top ought to be good enough (or inside a microwave oven).

Unfortunately microwave ovens are not particularly good Faraday cages at certain frequencies. You can usually make a mobile phone ring inside one. (do not power the microwave up!)