Electronics > RF, Microwave, Ham Radio

Can the power consumption of a RF receiver be lowered?

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Hey, I'm thinking about an outdoor hobby project of mine where I need a device to be listening on the 433,92 ISM band for occasional messages and process them on a microcontroller. I've been meaning to make my own PCB with a custom receiver circuit, and I've been looking at the MICRF211 IC to do the job. In the datasheet I noticed that it constantly draws about 6 mA of current when operating. This doesn't seem much at a first glance, but since the device is going to be powered by a battery and a small solar panel, it's a lot. The IC apparently **needs** this current to be able to listen at all times.

Is there a way to lower this consumption somehow without affecting the receiver's RF "attention"? A different RF IC maybe?
How are some other low-power receivers (BTLE?) designed so that they can reliably pickup messages, but don't constantly drain as much power?

Does the message have a detectable preamble, or does it repeat for a period of time?

I did a design which had the exact same issue some years ago. I had the microcontroller periodically power up the receiver and listen for carrier. If it's quiet, turn off the receiver again and wait half a second or so. If there's a signal, leave the receiver on for long enough to find the start of the next repeat of the message, and decode from there.

The duty cycle ends up dominated by the start-up time of the receiver, ie. how long does it take to power it on and reliably detect carrier if it's there. The duration of the transmission tells you how often you need to switch on for a listen, to be sure you don't miss anything.

In my case the transmitter was a radio key fob, and people tend to hold down the button until they get a response. A half second delay caused by the radio being switched off most of the time didn't matter.

6mA is not untypical for a 433MHz receiver. Some newer rx ICs have polling built-in which is woken by the preamble bit train. I used a MAX41473 in a recent design, although I didn't get the polling to work that reliably mainly because the legacy TX had a weird preamble.

BLE services advertise periodically, but only listen for a fixed period after an advertising packet is sent then the MCU returns to sleep. If you're actively receiving (i.e. scanning) power consumption is relatively high.

I think 6 mA for a UHF receiver sounds pretty good.  The general trick in these cases is to decide how much "latency" ie delay, you can handle and have your receiver powered only enough to meet your latency requirement- this can save enormous amounts of power.  i've worked on tracking system for animals where the requirement was to get a guaranteed update only every 100 hours- the power drain can get close to zero!   You can go through the arithmetic of what the probability of getting a given message, etc. and what your errors are- this sets the limits.   A powerful technique available these days is to have the timing provided by GPS- essentially perfect,  you can wake for 1 second per minute to listen , this take your 6 ma to 60 uA.  The trick is how precisely can you wake up and how short of a time can you stay awake- its all in the error budget of the timing.  Using a very low drift RTC like a DS3231 that you update daily can save power over having the GPS active continuously- this can make for some amazing low power links.

You don't want to effect the receiver's RF "attention". Does it mean that you don't let the receiver sleep when idle? Below recommendations are based on sleeping when idle.

If the transmitter sends periodic keep alive packets, you can sync receiver's wake up times with the transmitter and sleep when idle. But if the transmitter is something like a garage door opener and sends only on keypress, then you may use a RTC as suggested to sync with time. But this adds complexity to both transmitter and receiver. Is the transmitter also battery operated?

A BLE peripheral occasionally wakes up and sends advertisement packets. It consumes transmission current at this time. Then it listens for a while to see whether there is a connection request. It consumes reception current at this stage. If a central device is listening and want to connect, it connects immediately after receiving an advertisement packet. After the connection is established, peripheral doesn't go into sleep until it disconnects. If there is no connection, peripheral sleeps again. If the peripheral is a door opener and the central has permanent power, peripheral can wake up when button is pressed then sleep for a long time. If the peripheral is a temperature sensor, it can wake up every 10 seconds and send new measurement. If it is a beacon, it sends more frequently.


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