Wireless and Bluetooth features. What is it that you want to see?

[mohitgarg]

As part of my TS65 project, I'm looking to add wireless functionality to the board.

This thread is more general, to find out what features users would like to see in a Bluetooth wireless keyboard. Since my project is open-source, once I have the firmware support and electronic design completed, the wireless features should be easily made into an adapter board that can be used with existing keyboards.

I need to get answers to some simple questions and you are more than welcome to add more.

First, some background:
1. USB can supply 5V at 500mA once enumerated as a keyboard device, truly it can supply 2.5W.
2. Most barebone keyboards use around 40-50mA at 5V, which is 200mW - 250mW.
3. Bluetooth Low Energy (BLE - BT 4.0) uses around 25mA at 3.3V, which is 100mW (Taking into consideration of 5V to 3.3V stepdown efficiency)
4. Rest of the 2.15W (~430mA @ 5V) is available for the other bells and whistles as well as charging a battery if required.
5. Rechargeable AA batteries are about 1900mAh @ 1.2V (Typical) - Using two in series which is quite common for such applications, we can draw about 4.5W. Using a barebones keyboard with BLE and no backlighting/RGB we can get about 12 hours considering the efficiency of step-up conversion.
6. Li-ion/Li-Po batteries suitable for a portable keyboard would be about 2100mAh @ 3.7V - 7.77W, which should give around 21 hours of battery time on the the barebones BLE keyboard.

NOTE: I'm a bit lost as to how existing wireless boards last so long on battery. I would really appreciate an answer on this.


Questions:
1. What kind of battery would you like to see in a keyboard?
-- AA
-- Li-Ion/Li-Po
-- Doesn't matter
-- Other, please specify

2. Would you like to have the board the ability to charge over USB?
-- Yes
-- No
-- Doesn't matter

3. What would be the max acceptable charge time?
-- 1 hour
-- 2 hour
-- 4 hours
-- Over night charge (Around 8 )
-- Other, please specify

4. Due to limitations of USB a max of only 400mA can be used for charging a battery, this would mean a charge time of around 4 hours. Would you like the ability to charge via a dedicated charger (Such as one supplied with your phone)?
-- Yes
-- No
-- Doesn't matter

5. If your answer to 4 is yes, what would be your preferred method for charging using a dedicated charger?
-- Same connector used to connect to computer
-- Dedicated secondary USB port (micro or mini)
-- Barrel-style wall wort connector
-- Qi, wireless charging
-- Doesn't matter
-- Other, please specify

TIA

[Ray]

for wireless keyboards the MCU should be sleeping most of the time. And even if the keyboard is actually in use right now, most of the time a polling rate of 500Hz is not needed at all. While typing, 100Hz should be fine (wild guess here). Using the right MCU that has higher input impedance allows for larger than usual pullups, etc...
Using 5V only for charging also helps a bit.
The barebones wired keyboard just has no reason to try to save power, so it doesn't.

As for BLE I am surprised to see 100mWs. We don't need to transmit much data at all, so we should not be transmitting most of the time. That said, I have zero experience with any BT.

For your questions:
If you expect battery life less than a week, then definately not AAs. NiCd and NiMh are not meant to be partially discharged/charged again, but with low battery life everybody wants to charge sooner rather than later.

If a charger is supported (many commercial keyboards don't, but what is a new battery once a year?) USB should be the prime choice.

For LiPo even four hours of chargetime shouldn't be a dealbreaker, since there is no need to wait till it is low. Sure faster is better.
Can you try to negotiate more current when you declare yourself as a composite device rather than a keyboard? looks like you cannot get more than 500mA on a data port.
I would prefer the idea that a one port fits all purposes.