Long-term low-energy wireless communications solution?

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Hello everyone.

 

I'm in the process of building a brake light for my bike, which I would say is 85% complete now.

 

In Sweden there is a popular type of old military bikes called Kronan (see attached picture) that have a metal cylinder intended to house a small bicycle pump. That's where I'm going to put the battery+brake light assembly.

 

However, I just realized that maybe I could use this to help me dark winter mornings, when I'm looking for my bike at the bus station. Is there any good communications system that is pretty much always on, yet doesn't require much energy?

 

Either I have a separate small device with a button for when I want to turn on the brake light. I would like to be able to use my smartphone for it. But I guess that limits it to Bluetooth which, as far as I know, isn't very energy saving.

 

My idea is that I get off the bus in the morning, turn on the light by remote, find it, turn off the light, and then bike to university (with the accelerometer functionality turning on the light when I'm braking).

 

Ideas?

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Last Edited: Mon. Jan 21, 2019 - 05:57 AM
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Bluetooth should be low power enough methinks. Something like a nRF51 device. It is supported by Arduino and fairly straightforward to do a mobile app.

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Kartman wrote:
Bluetooth should be low power enough methinks. Something like a nRF51 device. It is supported by Arduino and fairly straightforward to do a mobile app.

 

I'll use a 2200mAh lithium battery, the longest I think it'll go between charges is a week. I'm using an ATTiny85 with a ADXL335 accelerometer (from this thread https://www.avrfreaks.net/forum/...). I guess if I change the connection of the accelerometer to be powered from a pin of the Tiny, then I could also control if it's on from the smartphone.

 

What do you think?

 

EDIT: Or maybe a PNP with the VCC and just control base current with the Tiny. 

Last Edited: Fri. Jan 18, 2019 - 09:21 AM
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Naccache wrote:
the longest I think it'll go between charges is a week.
You should be able to do the sums but consider some rough example numbers. The whole thing complete with Bluetooth probably consumes, at worst, an average 2mA. You have a 2200mAh battery so it will run for 1,100 hours. That is 45 days, which is 6.5 weeks.

 

Obviously it's key to work out what that "2mA" value really is and that depends what the entire circuit consists of and what it is up to. I'm guessing the AVR will actually sleep most of the time and just wake up every now and again to "sniff the airwaves". Similarly the Bluetooth shouldn't need to operate continuously either. If you Google "nRF51 current consumption" then it depends what it is doing but operation seems to generally be down in the 10's of uA region.

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based on what you said, an nRF52 would be the best as other suggested, perhaps you can start reading about how bluetooth evolved to be BLE "Bluetooth Low Energy". if you want to go commercial this is something else depends on what "cheap" you mean.

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Shame you don't have a hub dynamo.

If you did go the nRF5x route, you can lose the AVR, as the nRF5x is more than capable of handling the other tasks(i.e. reading the accel, turning on the light).

Four legs good, two legs bad, three legs stable.

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clawson wrote:

Naccache wrote:

the longest I think it'll go between charges is a week.

 

You should be able to do the sums but consider some rough example numbers. The whole thing complete with Bluetooth probably consumes, at worst, an average 2mA. You have a 2200mAh battery so it will run for 1,100 hours. That is 45 days, which is 6.5 weeks.

 

Obviously it's key to work out what that "2mA" value really is and that depends what the entire circuit consists of and what it is up to. I'm guessing the AVR will actually sleep most of the time and just wake up every now and again to "sniff the airwaves". Similarly the Bluetooth shouldn't need to operate continuously either. If you Google "nRF51 current consumption" then it depends what it is doing but operation seems to generally be down in the 10's of uA region.

 

What's your experience with HM-10 and power consumption? I'm guessing worse than the nRF5x?

 

 

Moe123 wrote:

based on what you said, an nRF52 would be the best as other suggested, perhaps you can start reading about how bluetooth evolved to be BLE "Bluetooth Low Energy". if you want to go commercial this is something else depends on what "cheap" you mean.

 

I guess so. I've used HM-10 and their chinese knock-offs a bit and am ok with the result I get from them. It's not commercial, just private use for fun.

 

 

John_A_Brown wrote:

Shame you don't have a hub dynamo.

If you did go the nRF5x route, you can lose the AVR, as the nRF5x is more than capable of handling the other tasks(i.e. reading the accel, turning on the light).

 

No, but I have a classic old style 6V, 3W fork-mounted dynamo like in the attached image :-)

 

Regarding the nRF5x route, I already have a circuit board now, and I already have some cheap chinese HM-10 knockoffs that I know work with BLE. I'll just have to see how much current they use.

 

If I were to change microcontroller. What do I need to program it, hardware- and software-wise? I use a Mac.

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As i said, nrf51 or 52 are supported by Arduino which runs on win/lin n mac. There’s also PlatformIO and MBED as well. All free. Late entry - Segger Embedded Studio - free for nrf. I did an app for the iphone. The bluetooth was the easy part as there was a little library to wrap the bluetooth.

Hardware wise, i started with the Nordic DK board. Now you can use the bbc micro-bit. That should have all you need.

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use Laird modules/ based of nRFxxxx, they spare you a lot of time, as for the library, they have one of the best libraries and you can develop your solutions using eclipse "open source", there is a documentation how to get started, a little bit of google would help.

 

Good luck!

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Naccache wrote:
... and I already have some cheap chinese HM-10 knockoffs that I know work with BLE. I'll just have to see how much current they use.

HM-10 Bluetooth 4 BLE Modules | Martyn Currey

...

 

Introduction

http://www.martyncurrey.com/hm-10-bluetooth-4ble-modules/#intro

...

HM-10 Basic specs

  • +2.5v to +3.3v
  • Requires up to 50mA
  • Uses around 9mA when in an active state
  • Use 50-200uA when asleep

...

via BLE / Bluetooth 4 | Martyn Currey

 

"Dare to be naïve." - Buckminster Fuller

This reply has been marked as the solution. 
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Have you looked at 433MHz TX/RX as used in garage door openers. There is a module HIR6-433A - RF MODULE, RECEIVER, AM, 433MHZ that says it uses less than 2mA. When a button is pressed on the transmitter, it raises an output line. Could be used to wake a processor from deep sleep. Claim up to 100m but that would be ideal conditions.

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Naccache wrote:
I'll use a 2200mAh lithium battery, ...
Nickel batteries can be recharged below freezing; so, can park the bike outside or in a cold garage or shed and still recharge the bike's battery (0.1C below freezing instead of 0.2C or 0.5C)

NiZn cells have greater voltage than NiMH (therefore fewer cells per battery) but don't reach 2200mAh for COTS cells.

Conrad energy HR06 AA battery (rechargeable) NiZn 1500 mAh 1.6 V 4 pc(s) from Conrad.com

 

"Dare to be naïve." - Buckminster Fuller

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Naccache wrote:
No, but I have a classic old style 6V, 3W fork-mounted dynamo like in the attached image :-)
https://www.youtube.com/watch?v=i7kgzgcqe5s

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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gchapman wrote:

Naccache wrote:

I'll use a 2200mAh lithium battery, ...

 

Nickel batteries can be recharged below freezing; so, can park the bike outside or in a cold garage or shed and still recharge the bike's battery (0.1C below freezing instead of 0.2C or 0.5C)

NiZn cells have greater voltage than NiMH (therefore fewer cells per battery) but don't reach 2200mAh for COTS cells.

Conrad energy HR06 AA battery (rechargeable) NiZn 1500 mAh 1.6 V 4 pc(s) from Conrad.com

 

How do you mean I should charge it? Also, I'm in Sweden (tomorrow is 15 below freezing :-)), so it's a different kind of cold I suppose. My idea is to have the unit easily removable and just charge at home overnight.

 

ajcashin wrote:

Have you looked at 433MHz TX/RX as used in garage door openers. There is a module HIR6-433A - RF MODULE, RECEIVER, AM, 433MHZ that says it uses less than 2mA. When a button is pressed on the transmitter, it raises an output line. Could be used to wake a processor from deep sleep. Claim up to 100m but that would be ideal conditions.

 

Now I have! I think that's going to be the solution. Seems easy and implementable.

 

joeymorin wrote:

Naccache wrote:
No, but I have a classic old style 6V, 3W fork-mounted dynamo like in the attached image :-)
https://www.youtube.com/watch?v=i7kgzgcqe5s

 

Hahaha... While I do love The Simpsons, this is not a realistic presentation of forkmounted dynamos ;-)

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ajcashin wrote:

Have you looked at 433MHz TX/RX as used in garage door openers. There is a module HIR6-433A - RF MODULE, RECEIVER, AM, 433MHZ that says it uses less than 2mA. When a button is pressed on the transmitter, it raises an output line. Could be used to wake a processor from deep sleep. Claim up to 100m but that would be ideal conditions.

Just checked out a datasheet - it reckons there's a version that consumes < 1mA

It is 5V, though, which could be a problem(if you haven't got 5V)

 

Four legs good, two legs bad, three legs stable.

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Since that tube that you are putting it in is metal, you will need some kind of external antenna!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Naccache wrote:
How do you mean I should charge it?
Oh

Naccache wrote:
... when I'm looking for my bike at the bus station.
I'm glad the ones of Sweden have overnight parking at public transportation; that's not available here (during the night, parked vehicles will be unlocked, towed, and impounded) (a sign on all light poles stating no overnight parking)

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

Naccache wrote:
How do you mean I should charge it?
Oh

Naccache wrote:
... when I'm looking for my bike at the bus station.
I'm glad the ones of Sweden have overnight parking at public transportation; that's not available here (during the night, parked vehicles will be unlocked, towed, and impounded) (a sign on all light poles stating no overnight parking)

 

 

I see, that's too bad. I've screencapped (from google maps) the bike stands at my regular bus stop and at the bus station. Since it's a university town, everyone gets around by bike. Usually I remember where I've put it, but like now when I'm coming back from the winter holidays, it's not so easy.

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Maybe one of these would help, at least until others copy you.

 

Jim

Click Link: Get Free Stock: Retire early! PM for strategy

share.robinhood.com/jamesc3274
get $5 free gold/silver https://www.onegold.com/join/713...

 

 

 

 

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Hey everyone! Just wanted to report in and say that the device is finished now. I've attached some pictures and the source code for anyone who might be interested.

 

Unfortunately, I didn't get the radio to behave well in the metal cylinder, so that part was scrapped.

 

Have a great weekend!

 

All the best, Christian

 

 

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Last Edited: Sat. Mar 23, 2019 - 08:04 PM