BLE, 3 mini questions

[OEMODM]

Hi everyone,

I'm new to Bluetooth Low energy and need to manage it's implementation to a bicycle speedo, to send km/h updates to android phone every second. 2 metre distance. I have 3 questions which from researching today being unable to find clear answers:

1. Question. What detail on a technical spec. outlines the consumption mA when a BLE is actually sending data to a phone, is it active TX + working current?
I've seen so many consumption modes: tx active, dormant, sleep, idle, standy, working current.
www.digikey.com/en/product-highlight/s/stmicroelectronics/bluenrg

2. If the BLE needs to "send km/h speed data" to the phone every second, does the BLE need to stay in Tx active mode all the time, or can he pop in & out of sleep mode to save power?
Probably a really stupid question.

2. Am I right? The distance of sending BLE data depends on the dBm value. The higher, the greater the distance. 0 dBm for 1 metre, 1 dBm for 2 metres. The dBm is determined by antenna size applied to the PCB surface.

sincerely / jack

 

[ronsimpson]

I did not look up you part but:
There usually are several different power modes.
transmit.
receive.
Awake but not transmitting or receiving.
Asleep and needs little time to wake up.
Asleep and needs much time to wake up. (much time might be mS or 10mS, not long in human years)

To save power you want to spend little time transmitting.
To save power you might want to not stay awake when not sending data. (depends on how long it takes to reconnect) You need to research this.

It is typical for the "low power" part to do as little thinking as possible. Maybe just send how many time the tire turned over in the last 1 second. Let the phone application convert that to km/hr.

Question:
Why use blue tooth? Can't the phone count rpm of the tire with out blue tooth?

 

[OEMODM]

Ronsimpson, thankyou. Understand most of your points. We need to use BLE for lots of reasons (reference to question). I understand most of what you said. I hope for answers to my specific questions or pointers to a forum which might if this is too specialist.

 

[Overclocked]

I have some notes to share. I had tested the common HC-05 bluetooth module for a datalogger. As far as transmission goes, at 9600 baud, the transmitter stayed on for 5 seconds and in those 5 seconds consumed 20mA. Idle current was around 2mA average. Obviously if you use a FET to turn on/off the bluetooth module, it will go down to nil, just give the BT link enough time to reestablish itself. You can set it to do so automatically by pairing them internally. For the HC05/06, this was done with AT+command.

 

[OEMODM]

Thanks overclocked. I'm hoping to find a BLE chip which can turn hop between sleep/idle and Tx active within 30ms. Thus, in 1 minute of sending data every second, it will be consuming Tx active current for < 25 seconds. Don't know if this is too aggressive.

 

[Overclocked]

Why that short of a period? I dont think you would get that much power savings by sleeping inbetween the space of 30mS. Now if you were sending data once every minute, then yes I would use low power mode on the bluetooth. Even a FET to control it would do the job as well.