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Data over battery line

Started by Marco Trapanese February 7, 2012
Hello,

I need to transmit few bits on a cable connected to the battery of a 
motorbike. The communication must be bidirectional. Very very low bit 
rate. The cable lenght is less than 2 m.

I'm thinking about a quite high-frequency PWM (about 100 kHz) with a 
simple on-off modulation. Passive detector on receiver side with a 
comparator.

Cost is the primary target thus I'd avoid to use a pll.

I'm wondering if the battery will "eat" the carrier, like a big 
capacitor. Because on the cable flows up to 30A it may cost a lot using 
inductors on battery side.

Any hint?

Marco
Do a google search for 1-wire.  Maxim and others make inexpensive
developers kits and interface products.


On Feb 7, 3:03=A0am, Marco Trapanese <marcotrapaneseNOS...@gmail.com>
wrote:
> Hello, > > I need to transmit few bits on a cable connected to the battery of a > motorbike. The communication must be bidirectional. Very very low bit > rate. The cable lenght is less than 2 m. > > I'm thinking about a quite high-frequency PWM (about 100 kHz) with a > simple on-off modulation. Passive detector on receiver side with a > comparator. > > Cost is the primary target thus I'd avoid to use a pll. > > I'm wondering if the battery will "eat" the carrier, like a big > capacitor. Because on the cable flows up to 30A it may cost a lot using > inductors on battery side. > > Any hint? > > Marco
On a sunny day (Tue, 07 Feb 2012 10:03:12 +0100) it happened Marco Trapanese
<marcotrapaneseNOSPAM@gmail.com> wrote in <jgqpcj$doj$1@tdi.cu.mi.it>:

>Hello, > >I need to transmit few bits on a cable connected to the battery of a >motorbike. The communication must be bidirectional. Very very low bit >rate. The cable lenght is less than 2 m. > >I'm thinking about a quite high-frequency PWM (about 100 kHz) with a >simple on-off modulation. Passive detector on receiver side with a >comparator. > >Cost is the primary target thus I'd avoid to use a pll. > >I'm wondering if the battery will "eat" the carrier, like a big >capacitor. Because on the cable flows up to 30A it may cost a lot using >inductors on battery side. > >Any hint?
At 100kHz you would nee an inductor to prevent the RF from shorting. Its resistance would be prohibitive at 30A. Maybe better use some of the shelf 430 MHz modules and go wireless? Or at least use a much higher frequency, 100 MHz or up. Sometimes an extra wire (copper) is the simplest solution, bet there is space where there is a 30 A conductor.
Il 07/02/2012 11:42, Jan Panteltje ha scritto:

> At 100kHz you would nee an inductor to prevent the RF from shorting. > Its resistance would be prohibitive at 30A.
I agree.
> Maybe better use some of the shelf 430 MHz modules and go wireless? > Or at least use a much higher frequency, 100 MHz or up. > Sometimes an extra wire (copper) is the simplest solution, > bet there is space where there is a 30 A conductor.
I know this, but the customer requires neither extra conductor nor wireless... So I'm looking for a solution, if any. Marco
"Marco Trapanese"  wrote in message news:jgqpcj$doj$1@tdi.cu.mi.it...
> >Hello, > >I need to transmit few bits on a cable connected to the battery of a >motorbike. The communication must be bidirectional. Very very low bit rate. >The cable lenght is less than 2 m. > >I'm thinking about a quite high-frequency PWM (about 100 kHz) with a simple >on-off modulation. Passive detector on receiver side with a comparator. > >Cost is the primary target thus I'd avoid to use a pll. > >I'm wondering if the battery will "eat" the carrier, like a big capacitor. >Because on the cable flows up to 30A it may cost a lot using inductors on >battery side. > >Any hint? > >Marco
Of course the battery will act as a capacitor.... that&rsquo;s what they effectively are. The issue is not the battery as that can be disconnected, it is the devices being power by the battery. They must have enough capacitance to deal with the added noise on the line. You just need a way to disconnect both ends(because of bi-dir) and put your comm stubs inbetween. device----+-------wire----------+----battery where the + are the comm stubs. Essentially you disconnect the wire when transmitting a low which causes the voltage to drop. Dealing with the switching, the high currents, etc really isn't worth it though. It doesn't cost much do add a 30AWG comm wire. It will be much cheaper, easier, and safer. (The above scheme is basically a TDM but 1 signal is actually power) You can get around some of the issues with switch by not completely disconnecting the wire(so your low is not 0V but maybe Vcc/2). Since you are not transmitting much data and you can do it at relatively high rates you do not need much capacitance added after the stubs. Just enough to keep the voltage from drooping too much during transmission. --
On Feb 7, 2:03=A0am, Marco Trapanese <marcotrapaneseNOS...@gmail.com>
wrote:
> Hello, > > I need to transmit few bits on a cable connected to the battery of a > motorbike. The communication must be bidirectional. Very very low bit > rate. The cable lenght is less than 2 m. > > I'm thinking about a quite high-frequency PWM (about 100 kHz) with a > simple on-off modulation. Passive detector on receiver side with a > comparator. > > Cost is the primary target thus I'd avoid to use a pll. > > I'm wondering if the battery will "eat" the carrier, like a big > capacitor. Because on the cable flows up to 30A it may cost a lot using > inductors on battery side. > > Any hint? > > Marco
Several ways come to mind .. the cheapest could be to use the 'implied' third wire and drive the two battery lines against it. Low bit rate?! I could do that at a distance of 2m for $.20 !!! Already did similar for a full-duplex wireless headset for the cellphone industry. Energy so low the test labs couldn't 'see' anything going on. Best solution will be determined by cost/volume requirements. Straightforward, is to insert band impedance between the battery and line and between the line and charging unit. Subtle is to take advantage of the impedance inside the battery, measured [I HATE garage designs, but low volume production they work!] and work against that. What is budget for parts? I know it can be done with less than $50/ link, but you may be thinking more a long the line of $.50/link. What ever you do keep in the frequency domain.
On Feb 7, 10:16=A0am, Robert Macy <robert.a.m...@gmail.com> wrote:
> On Feb 7, 2:03=A0am, Marco Trapanese <marcotrapaneseNOS...@gmail.com> > wrote: > > > > > > > Hello, > > > I need to transmit few bits on a cable connected to the battery of a > > motorbike. The communication must be bidirectional. Very very low bit > > rate. The cable lenght is less than 2 m. > > > I'm thinking about a quite high-frequency PWM (about 100 kHz) with a > > simple on-off modulation. Passive detector on receiver side with a > > comparator. > > > Cost is the primary target thus I'd avoid to use a pll. > > > I'm wondering if the battery will "eat" the carrier, like a big > > capacitor. Because on the cable flows up to 30A it may cost a lot using > > inductors on battery side. > > > Any hint? > > > Marco > > Several ways come to mind .. the cheapest could be to use the > 'implied' third wire and drive the two battery lines against it. > > Low bit rate?! I could do that at a distance of 2m for $.20 !!! > Already did similar for a full-duplex wireless headset for the > cellphone industry. Energy so low the test labs couldn't 'see' > anything going on. > > Best solution will be determined by cost/volume requirements. > > Straightforward, is to insert band impedance between the battery and > line and between the line and charging unit.
You mean an inductor in the line?
> > Subtle is to take advantage of the impedance inside the battery, > measured [I HATE garage designs, but low volume production they > work!] =A0and work against that.
I was wondering if he could use a resonant circuit. Put a series LC on the end and pick-off at the mid-point. Then amplitude modulate the 'signal'. George H.
> > What is budget for parts? =A0I know it can be done with less than $50/ > link, but you may be thinking more a long the line of $.50/link. > > What ever you do keep in the frequency domain.- Hide quoted text - > > - Show quoted text -
Il 07/02/2012 11:31, lektric.dan@gmail.com ha scritto:

> Do a google search for 1-wire. Maxim and others make inexpensive > developers kits and interface products.
I know 1-wire protocol. I'm concerned about the battery connected to the bus. Do you think it isn't affected? Marco
On Feb 7, 4:03=A0am, Marco Trapanese <marcotrapaneseNOS...@gmail.com>
wrote:
> Hello, > > I need to transmit few bits on a cable connected to the battery of a > motorbike. The communication must be bidirectional. Very very low bit > rate. The cable lenght is less than 2 m. > > I'm thinking about a quite high-frequency PWM (about 100 kHz) with a > simple on-off modulation. Passive detector on receiver side with a > comparator. > > Cost is the primary target thus I'd avoid to use a pll. > > I'm wondering if the battery will "eat" the carrier, like a big > capacitor. Because on the cable flows up to 30A it may cost a lot using > inductors on battery side. > > Any hint? > > Marco
The cable may be less than 2m but the line of sight distance should be more like 1m. Using some 555s, an opamp active bandpass at the carrier frequency (~100KHz band), and some ferrites, you can make an NFMI transceiver. It's done all the time for shortrange communication and low throughput telemetry systems. NFMI stands for Near Field Magnetic Induction, which just means magnetic field generation and pickup, usually using ferrite rods. These systems are relatively low power too, it doesn't take much to communicate over 1m.
On 2/8/2012 12:32 PM, Fred Bloggs wrote:
> On Feb 7, 4:03 am, Marco Trapanese<marcotrapaneseNOS...@gmail.com> > wrote: >> Hello, >> >> I need to transmit few bits on a cable connected to the battery of a >> motorbike. The communication must be bidirectional. Very very low bit >> rate. The cable lenght is less than 2 m. >> >> I'm thinking about a quite high-frequency PWM (about 100 kHz) with a >> simple on-off modulation. Passive detector on receiver side with a >> comparator. >> >> Cost is the primary target thus I'd avoid to use a pll. >> >> I'm wondering if the battery will "eat" the carrier, like a big >> capacitor. Because on the cable flows up to 30A it may cost a lot using >> inductors on battery side. >> >> Any hint? >> >> Marco > > The cable may be less than 2m but the line of sight distance should be > more like 1m. Using some 555s, an opamp active bandpass at the carrier > frequency (~100KHz band), and some ferrites, you can make an NFMI > transceiver. It's done all the time for shortrange communication and > low throughput telemetry systems. NFMI stands for Near Field Magnetic > Induction, which just means magnetic field generation and pickup, > usually using ferrite rods. These systems are relatively low power > too, it doesn't take much to communicate over 1m.
It would seem to me a 2m piece of wire and one-wire comm would be far easier.