Bluetooth power requirements.

[koti]

I’n thinking of doing a prototype of a remote bluetooth switch for a flashlight. The flashlight would have a BT module and a Li-Ion cell as a power source so there is no problem on this side, the switch would have to have a BT module and a small battery as a power source as well, I wonder if a small watch type CR2032 battery would be enough to power the BT module in the switch and perform switching? The distanse between the two devices would be 10cm at most. The switch has to do only on/off operation but a tiny battery indicator LED would be good too. What do you think? Will a small flat watch battery be enough to power this?

[Klaynos]

You'd need a Bluetooth module and probably a microprocessor to interpret the info and then a transistor as the switch. 

Outside pairing a hc-05 uses about 8mA you could run that at the voltage of the cr2032 along with say an Arduino pro micro 3.3V at around 5mA with no modifications. Cr2032 are typically in the region 250mAh, if we call it 260 mAh for simplicity, 260/13 is 20 hours. You can get the Arduino side down quite a bit but not sure how much better more expensive Bluetooth 4 devices will get you. 

[koti]

4 hours ago, Klaynos said:

You'd need a Bluetooth module and probably a microprocessor to interpret the info and then a transistor as the switch. 

Outside pairing a hc-05 uses about 8mA you could run that at the voltage of the cr2032 along with say an Arduino pro micro 3.3V at around 5mA with no modifications. Cr2032 are typically in the region 250mAh, if we call it 260 mAh for simplicity, 260/13 is 20 hours. You can get the Arduino side down quite a bit but not sure how much better more expensive Bluetooth 4 devices will get you. 

The hc-05 looks like its several times too large for this, I would need the whole thing on the switch side to fit into say 8mm x 5mm at most so maybe smartphone type smaller module? I also havent figured out yet how to do permanent pairing, I wonder if there might be another technology besides BT to do this, maybe NFC?

[Klaynos]

I used hc-05 as an example. Yeah torch tail switches are normally not too big. What host are you using? 

You could look at 433MHz transmitter receiver pairs. That plus an attiny85 surface mount on a bespoke PCB might just get down to the size required. 

I imagine the few lights that do this do it by having some more space and something on the mcpcb. 

What led are you using in your torch? The Samsung LH351D looks pretty interesting at the moment. 

[koti]

16 minutes ago, Klaynos said:

I used hc-05 as an example. Yeah torch tail switches are normally not too big. What host are you using? 

You could look at 433MHz transmitter receiver pairs. That plus an attiny85 surface mount on a bespoke PCB might just get down to the size required. 

I imagine the few lights that do this do it by having some more space and something on the mcpcb. 

What led are you using in your torch? The Samsung LH351D looks pretty interesting at the moment. 

I want to do this on a Surefire MD300 with a Malcoff head, its a small single CR123 light, the switch is a Surefire rifle switch, its all mounted on a Lewis Machine assault riffle. The LH351D unfortunately has a high Vf so its a no no at least for my current builds. 

[Klaynos]

I see, cool. Yeah it does. Also probably too floody for this application. 

433MHz modules are definitely worth a look. You can pretty much control the range with antenna length too. 

[koti]

10 hours ago, Klaynos said:

I see, cool. Yeah it does. Also probably too floody for this application. 

433MHz modules are definitely worth a look. You can pretty much control the range with antenna length too. 

Actually this emitter would be perfect if not for the high forward voltage. Its simiar in beam pattern to XPL but has a perfect, artifact less beam and very high CRi while producing simillar light intensity as the XPL. Its still great to use in multi cell applications where the voltage doesn’t drop so fast or with boost drivers. 

The range needs to be very short - switch on top of the gun on the barrel in the front and the light mounted just an inch or two away on the right side. I would need to squeeze the BT module and the chip either on the driver itself in the light (in the head) or in the tailcap. Switch will be even more of a problem because therese going to be even less room probably. The idea is to eliminate cabling between the light and the switch which cause problems when the soldiers operate inside buildings, the cables get in the way. 

[Sensei]

13 hours ago, koti said:

I wonder if there might be another technology besides BT to do this, maybe NFC?

NFC has 4 cm range...

https://en.wikipedia.org/wiki/Near-field_communication

"Near-field communication (NFC) is a set of communication protocols that enable two electronic devices, one of which is usually a portable device such as a smartphone, to establish communication by bringing them within 4 cm (1.6 in) of each other.[1]"

(other sources say about <= 10 cm, and <= 20 cm)

 

 

18 hours ago, koti said:

I’m thinking of doing a prototype of a remote bluetooth switch for a flashlight.

Buy remote controlled car toy or micro-drone-toy (the cheapest one you can get), remove everything unneeded, and you have essential stuff: button from remote controller, and circuit which can be on or off, on device. If batteries are enough for toy, after removing 95% of it (plastic body of toy), they will last longer.

 

Edited August 5, 2018 by Sensei

[koti]

10 minutes ago, Sensei said:

NFC has 4 cm range...

https://en.wikipedia.org/wiki/Near-field_communication

"Near-field communication (NFC) is a set of communication protocols that enable two electronic devices, one of which is usually a portable device such as a smartphone, to establish communication by bringing them within 4 cm (1.6 in) of each other.[1]"

(other sources say about <= 10 cm, and <= 20 cm)

 

 

Right, thanks for the info, I guesss NFC will not be useful for this application. 

[koti]

4 hours ago, Sensei said:

 

Buy remote controlled car toy or micro-drone-toy (the cheapest one you can get), remove everything unneeded, and you have essential stuff: button from remote controller, and circuit which can be on or off, on device. If batteries are enough for toy, after removing 95% of it (plastic body of toy), they will last longer.

 

Sounds like aan idea. I think I will need to start with deciding what micro chip I need to control the BT operation with, ATMEL has ATINY85 (I use these for flashlight firmware) but Im not sure this will be sufficient for BT operation as its got only 8 in/out ports and BT (4.0?) probably needs more. There are some higher models of the ATMEL chips out there but Im not sure they will fit onto the electronic boards in the flashlight and the switch, I guess I need to start with figuring this out.