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by n1ywb
Thu Nov 10, 2011 7:49 pm
Forum: General discussion
Topic: Absolute minimum voltage
Replies: 7
Views: 732

Re: Absolute minimum voltage

I guess I need to do my homework on NiMH, the full charge voltage is 1.4 and the full discharge is 1.1, or 4.4 for the pack of 4. Will the RPi run on 4.4 volts? What about the 5.6v from a fully charged pack?
by n1ywb
Thu Nov 10, 2011 7:43 pm
Forum: General discussion
Topic: Absolute minimum voltage
Replies: 7
Views: 732

Re: Absolute minimum voltage

<t>OK so the nominal supply voltage is +5V. But what\'s the absolute minimum? Presumably the device doesn\'t stop working at 4.9V. How low can you go?<br/> <br/> I ask because it would be nice to be able to power an RPi from 4 NiMH rechargeable cells, which only have a nominal voltage of 1.2V per ce...
by n1ywb
Sun Oct 30, 2011 2:13 pm
Forum: Other projects
Topic: car pc
Replies: 36
Views: 11032

Re: car pc

<r>Protecting electronics in a car is as simple as putting a transient voltage suppression diode accross the power terminals, like one of these bad boys: <URL url="http://search.digikey.com/us/e.....-ND/285933">http://search.digikey.com/us/e.....-ND/285933</URL><br/> <br/> It also provides reverse p...
by n1ywb
Thu Oct 20, 2011 7:21 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

Quote from netomx on October 20, 2011, 18:36
I could recommend you to try to use MikroC for your project.. it is extremely easy to program your PICs.

No thanks. I'm a professional C programmer and I use AVR chips, not PIC. My IDE of choice is VIM+BASH.
by n1ywb
Thu Oct 20, 2011 6:26 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>Quote from jmg123 on October 20, 2011, 18:33<br/> <URL url="http://jmri.sourceforge.net/he.....ocol.shtml">http://jmri.sourceforge.net/he.....ocol.shtml</URL>. This is the protocol that withrottle uses, so you should be able to rig up something yourself.<br/> <br/> You mentioning putting the rasp...
by n1ywb
Thu Oct 20, 2011 3:48 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>2-3 inches is super tiny, you're thinking of N scale or something. I'm using Lionel 0 Gauge, which is 1:48 scale; There's plenty of room for everything inside this loco. This is the one I'm using: <URL url="http://www.postwarlionel.com/c.....?ITEM=2338">http://www.postwarlionel.com/c.....?ITEM=23...
by n1ywb
Thu Oct 20, 2011 2:37 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<t>I was looking at JMRI. Since I'll have the RPi right in the loco I could run JMRI right on it and use WiThrottle or something to drive the loco over wifi. I'd have to write a JMRI plugin to talk to my homebrew controller though.<br/> <br/> Actually all I really want is WiThrottle; I wonder if I c...
by n1ywb
Wed Oct 19, 2011 6:33 pm
Forum: Other projects
Topic: GPIO level
Replies: 3
Views: 965

Re: GPIO level

Also blue and white LEDs have a Vf drop of like 3.5-ish volts, so you aren't going to drive one at all directly from 3.3v.

http://www.oksolar.com/led/led....._chart.htm
by n1ywb
Wed Oct 19, 2011 6:29 pm
Forum: Other projects
Topic: GPIO level
Replies: 3
Views: 965

Re: GPIO level

<r>Yeah depends what your driving. It won't drive a real 7400 series TTL chip, but many chips nowadays have wider input voltages to accomodate lower voltage logic.<br/> <br/> Most logic can't source current for squat but some chips, notably microcontrollers like PICs or AVRs, can sink a reasonable a...
by n1ywb
Mon Oct 17, 2011 2:37 pm
Forum: Other projects
Topic: Optimizing Linux for Flash memory.
Replies: 26
Views: 79370

Re: Optimizing Linux for Flash memory.

It would be a good idea to configure the system to minimize log verbosity to avoid thrashing the flash on every little log write. Or if you don't need to retain logs mount /var/log as a ramdisk.
by n1ywb
Sun Oct 16, 2011 3:31 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<t>After some soul searching I think I will use an AVR after all. The primary motivation is the externally clocked counter peripheral, which will make an excellent tachometer. I'm just sceptical that the RPi running Linux would be able to respond to the tach pulses fast enough, that motor spins pret...
by n1ywb
Thu Oct 13, 2011 2:15 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>I measured peak current draw on my loco's motor this morning at 12 amps. Granted most train transformers would probably experience severe voltage drop preventing the current from getting that high in practice. So not only is the TLE 5206-2 too small, but it's also discontinued and getting pretty ...
by n1ywb
Wed Oct 12, 2011 6:12 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

Quote from netomx on October 12, 2011, 18:22
You wanted a good H bridge? either build your own or TLE 5206-2

Thanks for the tip on that part, it looks to be perfect for my application, and cheap too ($6 at digikey).
by n1ywb
Wed Oct 12, 2011 4:59 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<t>Everybody please stop suggesting I use an external micro for the PWM. I heard you, thanks for the suggestions, but one of my specific goals for this project is to do the PWM in software on Linux.<br/> <br/> I'm a professional software engineer. I've programmed PIC assembly professionally and I've...
by n1ywb
Wed Oct 12, 2011 1:36 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<t>Quote from Gert van Loo on October 12, 2011, 09:46<br/> I have a project using L6203 driven straight from a 3V3 PIC using the PIC PWM. Works like a charm.<br/> But that does only 4A. You sure you need 5A? I have a 12V motor using 2A lifting 120K (albeit slow).<br/> <br/> <br/> Well, I guess I rea...
by n1ywb
Wed Oct 12, 2011 4:07 am
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

Here's an interesting paper on Linux real time performance with the PREEMPT_RT patches: http://versalogic.com/download.....chmark.pdf
by n1ywb
Wed Oct 12, 2011 3:46 am
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>Quote from ahven on October 11, 2011, 18:43<br/> Out of interest, I checked on hobbyist prices for model trains and tracks, I hoped a smaller pricetag for such tiny pieces <E>:)</E> (electronic) switch tracks can be 80 euros!<br/> <br/> Are you looking at HO scale? That's usually the cheapest. I ...
by n1ywb
Wed Oct 12, 2011 3:43 am
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>I want to have "real time linux PWM system" on my resume. Also I am a cheap bastard and I have very little time to do this so I want to keep part count and cost and complexity to the absolute minimum and having two CPUs in the darn thing would not be minimal when one could suffice. Developing for...
by n1ywb
Wed Oct 12, 2011 3:01 am
Forum: Other projects
Topic: Break out board (GPIO, SPI, I2C, and UART)
Replies: 189
Views: 23243

Re: Break out board (GPIO, SPI, I2C, and UART)

<t>Quote from jojopi on October 11, 2011, 22:57<br/> Quote from n1ywb on October 11, 2011, 18:35<br/> Now it's stuck in a poo-loop.<br/> <br/> <br/> Magic SysRq-n forces all realtime and high-priority tasks back to nice zero.<br/> <br/> A UART is very nice to have, but always less important than a R...
by n1ywb
Tue Oct 11, 2011 5:35 pm
Forum: Other projects
Topic: Break out board (GPIO, SPI, I2C, and UART)
Replies: 189
Views: 23243

Re: Break out board (GPIO, SPI, I2C, and UART)

<t>Let me add that having an RS232 serial port for console access is really critical to embedded Linux debugging. Here's why.<br/> <br/> You've written a realtime control process and scheduled it with real time priority. Great it preempts the entire system, even the kernel. Now it's stuck in a poo-l...
by n1ywb
Tue Oct 11, 2011 5:32 pm
Forum: Other projects
Topic: Break out board (GPIO, SPI, I2C, and UART)
Replies: 189
Views: 23243

Re: Break out board (GPIO, SPI, I2C, and UART)

http://www.ecrostech.com/Atmel...../index.htm

I have that and I like it. Something like that for the Rpi would be great. My only complaint is I think I would prefer solderless breadboard to perfboard.
by n1ywb
Tue Oct 11, 2011 4:27 pm
Forum: General discussion
Topic: What have we missed?
Replies: 286
Views: 27417

Re: What have we missed?

<t>Quote from Chris Tyler on September 13, 2011, 04:20<br/> A battery-backed real-time clock (RTC) could be really useful in a number of contexts. Most Linux distros assume that time is available from somewhere (typically RTC or network).<br/> <br/> If you have network, you can sync with NTP at boot...
by n1ywb
Tue Oct 11, 2011 4:24 pm
Forum: General discussion
Topic: What have we missed?
Replies: 286
Views: 27417

Re: What have we missed?

<t>PREEMPT_RT patch set.<br/> GPIO input interrupts.<br/> Kernel configuration tuned for real-time performance.<br/> <br/> This thing will be used in a million embedded controller applications where the above items will be highly desirable, and they should have no measurable impact on non-realtime u...
by n1ywb
Tue Oct 11, 2011 4:21 pm
Forum: Other projects
Topic: Model railroad control system
Replies: 26
Views: 7058

Re: Model railroad control system

<r>My Raspberry Pi dream is to add a computer controller to my vintage Lionel locomotives.<br/> <br/> The basic design would be to write a PWM program that uses GPIO pins to drive a power converter to control the motor, and use a tachometer on the motor as feedback to the PWM program, again via a GP...
by n1ywb
Tue Oct 11, 2011 3:47 am
Forum: General discussion
Topic: GPIO
Replies: 11
Views: 902

Re: GPIO

<t>Quote from malcolmh on August 4, 2011, 15:11<br/> "About 16" the good lady says. With that number, the possibilities are endless for both parallel and serial port types.<br/> <br/> To make this fly, though, the GPIOs would ideally need to have edge-detecting interrupts available.<br/> Does the Br...

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