Low Power Transmitter + Receiver - Page 1
Forum section: electronics / projects

author: fedimakni
author_rank: Regular Contributor
timestamp: August 11, 2021, 08:36:22 am
content: Hello,I am planning to design a device which contain (Master + multiple slaves) the communication protocole used between them is BLE.Currently my application require a both way communication between master and slaves, so the slave devices need to stay in a listening mode in order to catch data from the master and also send informations back.The slave devices will be a battery powered devices so putting them in sleep mode (in order to save power) will unable them from catching data from the master.I heard about wake up IC like AS3933 but their range is just around 5 meters. My application need around 50+ meters between slave and master.Do anyone have an idea about a better wake up IC or any other idea that i can base on to establish such a communication with the lowest power i can do?I'll be very thankful to any information.Thanks.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2021, 04:51:26 pm
content: How much latency is acceptable?For instance if 10 seconds of latency is acceptable, then each receiver could shut off for 9 seconds out of 10 after synchronizing with the master, which would save 90% of the power in standby.

author: janoc
author_rank: Super Contributor
timestamp: August 11, 2021, 08:06:01 pm
content: Well, if you want to use BLE (Bluetooth Low Energy), then your choice is pretty much given - you need a SoC that can run Bluetooth. Using a second radio "wakeup" IC will only complicate things, make it into an EMI nightmare and likely eat your batteries faster than just sleeping the BLE SoC.There are plenty of decent BLE-capable SoCs, e.g. Nordic's nrf52 series.The achievable range is more a matter of what kind of antenna you use with it because the transmitting power is limited by both the BLE spec and the governmental regulations.Chip or PCB antenna will probably manage a ~10m-100m, "rubber duck" external one even the 400m the BLE specs talks about.And then it also depends on the environment - BLE means you are competing with other devices in the 2.4GHz band - wifi, Bluetooth, microwave ovens, etc. so the achievable range will be very different in an open field somewhere and in a busy shopping center or condo.If you have a large network you may want to look also into Bluetooth Mesh, then one device could relay packets for another and extend the range of the network significantly - at the expense of power consumption and mainly bandwidth available.Or look at a different protocol completely - maybe something like Zigbee or Thread would be more appropriate?Also you speak about low power - how low is low? Are we speaking about 100mA? 10mA? 100uA? 10uA?E.g. the Nordic nrf52840 runs at about 10mA, even when actively transmitting. When sleeping it is down to some nA but you can't sleep and expect the Bluetooth link to stay up. The reconnection latencies can be significant. Bluetooth Mesh has a feature that lets another device to act as a "friend" for a low power device that sleeps most of the time and communicate on its behalf - but you still need a nearby (as in radio range) device that is not sleeping for it to work. Etc.You gave too little information to give you a meaningful answer.

author: fedimakni
author_rank: Regular Contributor
timestamp: August 12, 2021, 04:48:28 am
content: Hello,Thanks for the reply. Actually i am planning to use the nrf52832 in this application so the low power we plan to reach is in the uA range in sleep mode and few mA while transmitting. While checking the AS3933 you can notice that in the listening mode (waiting for a packet from master it consumes few uA which is very good as a wake up IC for a low power product) but the range is very small and it can only listen to few meters. That's why i was looking for other alternatives which can help to achieve such a goal. especially when communication in both side is necessary.

author: janoc
author_rank: Super Contributor
timestamp: August 12, 2021, 10:21:09 pm
content: I have measured the nrf52840 in sleep mode and the current draw was in the uA range. The specs says:QuoteJust have it wake up periodically (e.g. using the RTC) instead of waiting for a packet - you need to do that anyway if you want to keep the BLE link from timing out.You will have perhaps higher latency (if you happen to send a packet just as the slave has gone to sleep) but much simpler construction, fewer problems with interference and won't need to deal with BLE idiosyncracies because BLE isn't designed to allow the device to sleep while maintaining connection state (and the Nordic SoCs won't retain memory in those deep sleep modes anyway).