Bluetooth thing, what to buy and power source questions

Hi,

I want to do a bluetooth 2.1 thing and I need a little advice because I don't know what to buy. for what I've seen there are two options:

  1. buying the normal usb arduino then buying the bluetooth chip and connecting it to arduino by myself
    pros: more flexible (usb is more universal), I can use any bt chip, cheaper (but without adding bt chip price which would probably have an awful shipping cost), there are packs with arduino + testing components for a cheaper price than the two separate products.
    cost: arduino + component pack 43€

  2. buying arduino bluetooth which comes with bt integrated.
    pros: easier, don't need to search/buy a separate bt chip (I don't know if they would even sell you only 1 unit)
    cost: arduino bt 80€

What would you do? perhaps you have more information than me :stuck_out_tongue:

Another question: Are this bluetooth solutions suited for being powered by a coin cell or are they too power hungry? this thing I want to build doesn't need fast or continuous transmission. The bt chip should have a low power mode or something like that , I DONT KNOW!!! :.

Thanks!!

If you can do some solder work, i have few blank pcb's for cheap bluetooth integrated boards.

This may be the cheapest solution:
http://www.dealextreme.com/p/jy-mcu-arduino-bluetooth-wireless-serial-port-module-104299
Easy to integrate with any Arduino.

Just as a point of comparison, I am currently using an ITead bluetooth shield (which I got mainly to avoid dealing with figuring out pinouts and soldering), and it works, but took a while to understand how to use correctly. Here’s my bluetooth story so far:

http://home.comcast.net/~tomhorsley/hardware/arduino/ITead.html

There is a link in there to the “missing datasheet info” I’ve figured out while using it.

I suspect that I would indeed have been better off getting one of the bluetooth modules recommended above that already has the pins soldered to it for simple breadboarding.

AoiAR:
I want to do a bluetooth 2.1 thing

What is the function you want to do? Not all Bluetooth radios are alike. There are different profiles for different applications in the Bluetooth standard.

AoiAR:

  1. buying the normal usb arduino then buying the bluetooth chip and connecting it to arduino by myself
    pros: more flexible (usb is more universal)

The word “universal” in “universial serial bus” doesn’t mean what you think. Each BT radio will require its own device drivers, few of which exist for the Arduino. So you’ll be writing custom code for whatever device you find. Which means you’ll have a USB Stack running a Bluetooth Stack and then doing what? That’s a lot to ask for in Arduino’s 2K of RAM.

AoiAR:
2. buying arduino bluetooth which comes with bt integrated.

This is an option if your want your Bluetooth “thing” to be a virtual serial port.

AoiAR:
Another question: Are this bluetooth solutions suited for being powered by a coin cell

Far from it. Long term current draw from a coin cell is less than 5mA. That’s more current than what just the ATmega328 draws.

Thanks for the answers.

What I want to do is similar to a remote keyboard, I don’t want to mix USB with BT , what I meant is that having an USB interface while you are prototyping looks like more flexible, to program the chip etc, the final version wouldn’t need USB.

As for the power issue I was searching a little and saw this:

In the Atmega328 datasheet:

Power Consumption at 1MHz, 1.8V, 25°C
– Active Mode: 0.2mA
– Power-down Mode: 0.1?A
– Power-save Mode: 0.75?A (Including 32kHz RTC) (0.00075mA)

And from Energizer cr2032 datasheet (3V 250mAh Li Ion button cell battery) :
with a load of 68,000 Ohm, drains 0.043 mA for 721h (30 days) at ~3V

If at the 3V of the cell (roughly double of 1.8v) and more than 1Mhz the chip drains 0.4mA in active mode instead of 0.2 it looks like it would
discharge about 10 times faster or in 72h since 0.4mA is 10 times more than 0.043mA (the sample load from energizer) very roughly

But my application only needs non continuous transmission so the chip would be in power save or power down mode most of the time.

I saw this guy disabling many things inside the chip and getting it to “work” with as little as 1 micro ampere and a coin cell:
http://www.sparkfun.com/tutorials/309

of course for my application there is also the bluetooth chips… I was searching information about this JY-MCU one but I don’t
see which IC’s it uses or any info about power consumption, anyway, powering the atmega + bt with just a coin cell doesn’t
look very doable… :frowning:

thanks.

bluetooth chip is bc417. it draw 30-40mA current when not paired and about 5mA after pairing. it have somekind of sleep mode but i dont know how sleepmode works.
i noticed if voltage for bt module drops below 3v it is not stable anymore so it perhaps dont work well with 3V coincell.

use google for datasheet >> linvor datasheet or hc05 datasheet

JY-MCU use 5v and have 3.3v regulator for module.

AoiAR:
What I want to do is similar to a remote keyboard, I don't want to mix USB with BT

There are BT Radios which are designed for the HID profile. You should be looking at one of those. It will significantly reduce the amount of code you have to write (and your Arduino has to run.)

Such as this one:

AoiAR:
As for the power issue I was searching a little and saw this:

In the Atmega328 datasheet:

Power Consumption at 1MHz, 1.8V, 25°C
– Active Mode: 0.2mA
– Power-down Mode: 0.1?A
– Power-save Mode: 0.75?A (Including 32kHz RTC) (0.00075mA)

So active mode of the ATmega328 by itself is drawing 0.2mA @ 1MHz. Keep in mind that none of the Arduino libraries support 1MHz natively. So you'll have some re-working ahead of you if need to use anything timer-based (millis, delay, pwm, spi communication, etc.)

AoiAR:
And from Energizer cr2032 datasheet (3V 250mAh Li Ion button cell battery) :
with a load of 68,000 Ohm, drains 0.043 mA for 721h (30 days) at ~3V

So what? What do you care what the life is at 0.043mA? Look at the graph right below that one, "Pulse Discharge Characteristics." Continous drain at 0.2mA is 225 Hours. The battery can withstand pulses into the 5-7mA range for up to 2 seconds, with a drop down to 2.8V. So life in a 5mA "pulse" application (sleep-wake up-sleep) is 200 Hours or so (8 days).

AoiAR:
But my application only needs non continuous transmission so the chip would be in power save or power down mode most of the time.

You are completely focused on the wrong component. The bluetooth radio is what will require large current consumption, not the tiny ATmega328. The HID Bluetooth module I linked to above has current consumption in the range of 12-40mA.

Getting an ATmega328 to run on a coin cell is certainly possible (not an Arduino board, but just the micro). Running a (relatively) high power RF radio off one? That's an extreme challenge.

Hi,

Hmm, that module you pointed out looks nice. I didn't think a radio like that would draw so much current. It really looks outside of coin cell capabilities.. In the prototype I want to build, the emitting antenna would be near the receiving one, just 1mm or 2 apart.. I'm wondering if that could be used to use less power someway, or with other product... The coin cell idea is really the only that appeals to me right now mainly because of space limitations and that's why I'm trying to find some way of doing it that way. I also found a SoC from texas instruments that is suitable for use with coin cells but it's for Bluetooth Low Energy / BT 4.0 and the hosts I want to connect to are Bluetooth 2.1 or less. This SoC isn't backward compatible so it isn't an option.. :S

You’re going to have a hard time finding a generic module that is ultra low power. Think about Bluetooth headsets. Everything in that product is designed specifically for that application. Off the shelf modules need extra features to appeal to a broader market. In most cases, those “off the shelf” applications have a relatively large power supply available (key word: relatively).

Why not look into a lipo battery? They can be quite small, decent capacity and are plenty good for short term power draw

Hi,

For prototyping I'm ok without a low power solution but I want to be sure this can be done before I start to spend more time/money into it. I've been reading about LiPo batteries and they look nice, high discharge rates and high power density. They even sell them in stackable thin films in various formats. The problem is that they look harder to handle safely but I think they could be a solution to my problem eventually. I've found this one for example:

It's very small (just 1mm thikness) and with 200mAh capacity, continuous discharge at 3V at 0.2C should give 40mA for 4 hours If i'm understanding it well. And with pulsed discharge who knows, there isn't info in the datasheet or I don't see it, but as a crude estimate with the info from the energizer cell that gave 7mA/0.2mA = 35 times more current (but pulsed) in the same time (more or less), then this would last perhaps 35 times more with the same 40mA but pulsed, or 140h.. again very roughly.. it isn't even the same technology. Also the pulsed data in the coin cell was for 2 seconds pulse X 12 times a day, perhaps not comparable with what a keyboard for casual use would spend (probably more).

Thanks for all the info, I'm going to buy the USB arduino plus the jy-mcu bluetooth module and probably also the one with the HID profile later.