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by RichC
Sat Jan 14, 2012 9:30 pm
Forum: HATs and other add-ons
Topic: Gertboard
Replies: 258
Views: 119081

Re: Gertboard

Hi Gert - I recommend an mbed http://mbed.org

It uses an NXP (Philips) micro with ARM Cortex-M3, lots of different I/O with drivers, and online compiler so no hassle installing tools.

Rich
by RichC
Wed Jan 11, 2012 1:05 pm
Forum: Other projects
Topic: Big Track and Raspberry Pi
Replies: 4
Views: 2470

Re: Big Track and Raspberry Pi

<r>I got a 2010 release Bigtrak for Christmas so now I have to mod it.<br/> <br/> My first challenge was the power supply:<br/> <br/> As standard it's powered by 3 x D cells. The two drive motors each pull 140mA typical and up to about 450mA at start-up. There is a resettable fuse on the control boa...
by RichC
Wed Jan 11, 2012 12:38 pm
Forum: Other projects
Topic: Raspberry PI and Zigbee
Replies: 13
Views: 30366

Re: Raspberry PI and Zigbee

You should be able to get started quickly with a Zigbee module from Farnell/Digikey. I was looking into them a few years ago and there seemed to be enough data and development kits.

Do you have a project in mind?
by RichC
Wed Dec 21, 2011 5:50 pm
Forum: General discussion
Topic: GCE A-Level (UK)
Replies: 25
Views: 5216

Re: GCE A-Level (UK)

<t>[quote]1. Requirements capture. What do you want it to do. Constraints?[/quote]<br/> <br/> Requirements are key. I did a couple of projects with a school and was very impressed with the student\'s take on the requirements. If you don\'t know what you want to build, how do you know when you\'ve do...
by RichC
Thu Dec 15, 2011 12:00 am
Forum: Other projects
Topic: How to add clock backed by battery?
Replies: 24
Views: 9794

Re: How to add clock backed by battery?

<t>You don't have to use a battery; for shorter backup times you could use a relatively cheap 0.1 Farad capacitor. Q = It = 0.5CV^2 so if you have 1V difference between normal supply and minimum standby, 0.1 farad and 1 microamp gives 13 hours backup.<br/> <br/> RTC 32.768kHz watch crystals used to ...
by RichC
Wed Dec 07, 2011 10:50 pm
Forum: Other projects
Topic: JTAG adapter
Replies: 12
Views: 19750

Re: JTAG adapter

<r>It has an ARM1176JZF-S core and unfortunately Keil ULINK does not support ARM11 - a choice ARM made when they bought Keil. You could use RealView ICE or Lauterbach, both quite expensive. Don't know about IAR.<br/> <br/> The ARM JTAG pins are shared with GPIO so you have to solder on a connector a...
by RichC
Tue Dec 06, 2011 6:14 pm
Forum: Other projects
Topic: Some kind of BASIC?
Replies: 12
Views: 3172

Re: Some kind of BASIC?

<t>Yes, you could have an SD card option so the Raspberry Pi boots to BASIC or some other language. One that can handle multimedia like audio/photos/videos and interact with web pages would be nice... I'm thinking Java because of its libraries and documentation, but learning OO might be a big ask.<b...
by RichC
Mon Nov 28, 2011 6:10 pm
Forum: Other projects
Topic: Controlling a mains power socket switch? (home automation)
Replies: 174
Views: 66217

Re: Controlling a mains power socket switch? (home automation)

<t>Relays are not always the best tool for the job. Okay, they're simple and can be rated for mains power, but the contacts can degrade and stick when when switching inductive loads. The right kind of contacts and a protection circuit help.<br/> <br/> Years ago my ex company designed a small machine...
by RichC
Mon Nov 28, 2011 5:43 pm
Forum: Other projects
Topic: Remote reboot switch
Replies: 25
Views: 8403

Re: Remote reboot switch

8mA would just drive a reed relay (12V 1.5K coil) but I cannot recommend it, because the voltage spike when you switch off the coil could destroy your Pi.

Just add a transistor like this. It's only a few pence more and it lets you select from a wider range of relays.
by RichC
Mon Nov 28, 2011 3:16 pm
Forum: Other projects
Topic: Remote reboot switch
Replies: 25
Views: 8403

Re: Remote reboot switch

<r>The GPIO has a default 8mA drive strength and it is characterised for 2mA with a 2.7V supply. That is:<br/> VOL (output low voltage) is 0.15V max at 2mA.<br/> VOH (output high voltage) is 2.50V min at 2mA (approx 2.8V min in practise because the R.Pi uses a 3.3V supply)<br/> <br/> This should be ...
by RichC
Sun Nov 27, 2011 9:38 pm
Forum: Other projects
Topic: Remote reboot switch
Replies: 25
Views: 8403

Re: Remote reboot switch

<t>Looks like that opto wants 10ma thru its input<br/> No. The datasheet has a section for "Current Transfer Ratio" and gives figures for 10mA and 1.0mA, and the graphs on page 5 show IF working down to 0.1mA although less efficiently. For example 1.0mA in gives minimum 34mA out.<br/> <br/> This was...
by RichC
Sun Nov 27, 2011 8:40 pm
Forum: Other projects
Topic: Remote reboot switch
Replies: 25
Views: 8403

Re: Remote reboot switch

<r>Interesting question so I looked at a datasheet. I think it'll be okay.<br/> <br/> Vishay CNY17-3 optocoupler (23p each from Rapid Electronics) datasheet <URL url="http://www.rapidonline.com/pdf.....8-0886.pdf">http://www.rapidonline.com/pdf.....8-0886.pdf</URL><br/> <br/> The LED's VF is typical...
by RichC
Thu Nov 17, 2011 3:29 pm
Forum: Other projects
Topic: Orbiter.
Replies: 51
Views: 12358

Re: Orbiter.

Very very difficult but do-able. A home-built rocket got to 121,000 feet recently...
feature=share
http://ddeville.com/derek/Qu8k.html
by RichC
Fri Oct 28, 2011 1:31 pm
Forum: General discussion
Topic: Wishes for 2nd gen Raspberry Pi
Replies: 272
Views: 79063

Re: Wishes for 2nd gen Raspberry Pi

<t>A true serial port - I know there's a UART port port but a straight RS 232 port would be great for various projects.<br/> RS232 would be nice - there are still loads of devices and sensors that use RS232 out there. The downside is extra board area and cost for a DB9 connector, MAX232 chip and cap...
by RichC
Thu Oct 27, 2011 2:07 pm
Forum: General discussion
Topic: Wishes for 2nd gen Raspberry Pi
Replies: 272
Views: 79063

Re: Wishes for 2nd gen Raspberry Pi

<r>HD44780 is for small LCDs such as 16x2 character, more useful for embedded devices. I've just bought a 20x4 character blue LCD to display fan speeds etc <URL url="http://lcdsmartie.sourceforge.net/">http://lcdsmartie.sourceforge.net/</URL> and it came without a connector, so some soldering is req...
by RichC
Wed Oct 12, 2011 12:41 pm
Forum: Other projects
Topic: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced
Replies: 239
Views: 278154

Re: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced

<r>Sounds like a nasty real-world problem that students could learn from <E>:)</E><br/> <br/> I've put a few thoughts in a wiki <URL url="http://rpiplc.wikispaces.com/Hardware">http://rpiplc.wikispaces.com/Hardware</URL> (as provided by ErvKosch, thanks).<br/> <br/> I think use SPI for the I/O bus b...
by RichC
Mon Oct 10, 2011 9:26 pm
Forum: General discussion
Topic: How would you use a Raspberry Pi device?
Replies: 514
Views: 235883

Re: How would you use a Raspberry Pi device?

I'd like to connect a USB webcam and continue a project I started a few years ago: a robot submarine.

The plan is I'd have a swarm of micro subs on a coral reef in Fiji, and people/students in the UK could log in and use the subs to cruise the coral or operate science packages.
by RichC
Fri Oct 07, 2011 8:01 pm
Forum: Other projects
Topic: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced
Replies: 239
Views: 278154

Re: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced

<t>Quote from Svartalf on October 7, 2011, 18:33<br/> Many PLC systems use an external watchdog setup to ensure you can't turn the thing off (which is possible with most of the on-board ones...)- and be able to do a bit more sophisticated things on a restart.<br/> <br/> Yes. An external watchdog giv...
by RichC
Fri Oct 07, 2011 12:26 pm
Forum: Other projects
Topic: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced
Replies: 239
Views: 278154

Re: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced

Re watchdog - that datasheet is for an ARM test chip, not an ARM core, and it refers to a watchdog peripheral. There is not a watchdog inside the ARM11 core.

If you need battery backup for the time & date, you could use a real-time clock chip with a watchdog in it.
by RichC
Wed Oct 05, 2011 10:30 pm
Forum: Other projects
Topic: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced
Replies: 239
Views: 278154

Re: Turn Raspberry Pi into a P.L.C (Programable Logic Controller) Advanced

<r>The I/O is key here. An industrial control system needs lots of different I/O types, many systems have a lot of sensors and actuators, and it must be fast and reliable. So you probably need to start with a bus design that can scale up. I2C sounds good but is it fast enough at 100 - 400kHz?<br/> <...

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