Raspberry Pi: Another Homebrew Prototyping Breadboard

I modified a prototyping breadboard that I had originally build for prototyping Microchip PIC devices by adding a Raspberry Pi. As what I have done may give people some ideas for homebrewing their own out of junk box parts, I will describe it a bit more.

As described in my discussion of another prototyping board, I like to have things securely fastened down so that you don't accidentally knock something out of whack, and you can pick the whole thing up and move it around. The only "moving parts" are the wires and components plugged into the solderless Breadboard / Proto Board units.

You can see where I mounted the rPI to a small aluminum plate (made from some scrapped electronic device chassis) using insulated grooved washers (to keep from shorting connections on the bottom). The plate is in turn screwed to the front bezel of the prototyping board. I used an Adafruit Pi Cobbler Breakout + Cable to get from the rPI GPIO pins to the proto board.

In my normal manner of scrounge and re-use, the main chassis is made from an old CD player that I found on the side of the road.

In the lower left front corner is the original power switch, which switches the original power cord to a +/- power supply inside consisting of a center tapped transformer, bridge rectifier, electrolytic filter capacitors. I use 3 terminal regulators to produce +3.3, +5, +12 and -12 voltages (most commonly needed for circuits). On the lower right front panel are 6 LEDS monitoring the unregulated and regulated voltages. You can find schematics for this type of regulated analog power supply all over the internet. Just be VERY careful working on the 120 volt primary side, heat shrink or tape all exposed connections as 120 volts can KILL YOU INSTANTLY. If you do not have the knowledge and skills to work with high voltages, buy pre-build power supplies to be safe.

The raspberry PI is actually powered by a separate +5 volt power supply out of the picture. Make sure that since the rPI GPIO pins as 3.3 volts, that you use all 3.3. volt circuits, OR do proper level conversion.

On the left hand top from the bottom are 8 leds that can be used to monitor a byte on the proto board. Above that are 4 LEDS to monitor the regulated +5 (2 supplies), +12 and -12 switched power to the board, with the switch just above that.

Above the power switch are a couple of switches and a connector that used to be used for a PIC programmer (no longer supported so removed). In it's place on the upper left corner is a Parallax 2 x 16 Serial LCD, very handy for monitoring and troubleshooting 5 volt TTL serial interfaces.

Along the top edge are 4 uncommitted binding posts, good from bringing leads from test equipment, etc. on board.

On the upper right is an LCD display using the parallel Hitachi HD44780 LCD controller (pretty much an "industry standard"). It is easy to interface this with a rPI or PIC/PICAXE.

Below that is a couple of knobs for LCD contrast, and speaker volume (small speaker on the side).

Below that are two knobs with 10K pots from +V to gnd to generate analog voltages.

Below that are 12 toggle switches and 2 push button switches to generate digital test signals.

Down both sides of the large white/blue proto board in the middle are proto pins on paddle boards that connect to the signals coming to/from underneath from the power, LCD, pots, switches, etc. These paddle boards were cut from a surplus proto board that plugged into the ancient IBM PC bus, so this would be hard to find. You could fabricate something similar with multiple  Adafruit Pi Cobbler Breakout + Cable, I suppose.

Note also that I have lots of Electrolytic and Ceramic bypass/decoupling capacitors plugged in on the power busses of the proto boards to provide transient suppression, this is VERY important for circuit stability. A lot of newbies leave these out, and end up with flaky operation of their circuits.

So as you can see, this prototyping breadboard provides a good solid base with lots of I/O devices for different experiments, without a ton of loose wires and parts lying all over the workbench. That makes if very hard to troubleshoot problems with your circuit.

Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi: 37 Sensors and Output devices for less than $100

I saw this in my daily eBay alert, and just HAD to post it (already ordered one :-)
I will copy the pertinent information directly from the listing (with some interesting translation, note that the "hydrargyrum-switch sensor" is probably a "mercury-switch sensor").

This is the seller's "store" in case the listing goes away, they have a lot of other interesting stuff, including Arduino):

_______________________________________________________

New SunFounder 37 modules Raspberry Pi Sensor Kit ,T-Cobbler

This new 37 Modules Sensor Kit provides all kinds of funny and completed modules for Raspberry Pi open source fans. These modules will output valuable signals directly by connecting Raspberry Pi Board. It is extremely easy for RPi fancier to control and use these modules. This kit will help you control the physical world with sensors.

Specification:

1.Passive Buzzer Module
2.common-cathode RED&GREEN LED Module
3.Knock sensor module
4.Shock-switch sensor Module
5.Photo resistor sensor Module
6.Push button Module
7.tilt-switch Module
8.RGB LED Module
9.infrared-transmit Module
10.RGB LED Module
11.hydrargyrum-switch sensor Module
12.two-color commoncathode LED Module
13.Active buzzer Module
14.Analog-temperature sensor Module
15.Colorful Auto-flash Module
16.Magnet-ring sensor Module
17.Hall sensor Module
18.Infrared-receive sensor Module
19.Analogy-Hall sensor Module
20.Magic-ring Module
21.Rotate-encode Module
22.Light break sensor Module
23.Finger-Pulse sensor Module
24.Magnetic spring Module
25.Obstacle avoidance sensor Module
26.Tracking sensor Module
27.Microphone sensor Module
28.Laser-transmit Module
29.Relay Module
30.18b20 temperature sensor Module
31.Digital-Temperature sensor Module
32.Linear-Hall Sensor Module
33.Flame sensor Module
34.High-sensitive voice sensor Module
35.humiture sensor Module
36.Joystick PS2 Module
37.touch sensor Module
38.400 Point Breadboard
39.Jump Wire x65
40.T-Cobbler with 26-Pin GPIO Cable
_______________________________________________________

Looks like a pretty good deal, free shipping from Hong Kong. If you had to go and source all of those items separately, would cost a lot more I am sure (if you could even get them in one of quantities).

I have bought a number of items from Hong Kong (even some from mainland China) without a problem, although shipping times can be a bit long. If it is a no show, eBay will refund you anyway (if you meet all the terms and conditions).

When I get it I will post a review.

EDIT 1: I actually found a review here for the Arduino version of the package. Looks like the hardware is not too bad, but documentation a little skimpy and code samples not the best.

EDIT 2: I received this item in about 2 weeks. Here is the box they came in:

Here is the rather meager documentation. The small item in the lower left is a little booklet that gives the pinouts for each device:

And here are the contents of the box spread out on the table:

The sensors all look of reasonable quality parts and workmanship, the raspberry pi to breadboard adapter does not fit perfectly to the small breadboard power supply rails, I had to bend the power supply pins a bit to make it fit, but it seems to connect. I ended up taking off the yellow plastic spacers and bending the pins 30 degrees one way, then back and the fit is better:

There is a website referenced in the documents  www.sunfounder.com  but there does not seem to be anything there. I emailed the seller, and he responded within a day that there is no specific documentation and code examples for the Raspberry Pi (they are working on it). The only documentation is the version for the Arduino:

Vendor Documentation Here

I have taken a look at it, and there is a detailed PDF that describes each part, and gives some example Arduino code. By reverse engineering the Arduino code, you should be able to get them working on a Raspberry Pi with the language of your choice, but this is not a project for the newbie, IMHO. Some of the sensors are a simple digital 1/0 value, others are an analog value and others are a more complex protocol. When I get some code going, I will post it here.

Also make note that they all seem to be 5 volt supply and signals, so you will have to convert the logic levels from 3.3 to 5 volts. Also, the Raspberry Pi does not have direct Analog inputs, so you will have to use an external PICAXE or another A/D converter chip. 

He also offered to replace the breadboard adapter, but I don't think that I will bother at this time. I have to admit that I was rather amazed by the speedy and friendly email response, the vendor is clearly trying hard to provide customer satisfaction. 



Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry PI - Home Brew Breadboard

I thought I would make a few notes about the Breadboard that I am using to experiment with hardware and software for my rPI, as it might give some newbies out there some ideas.

Building electronic breadboards is something I have been doing since grade 6 or 7 (in the 60's!) and I find that it is very important to help you build reliable and repeatable prototypes and keep from blowing things up.

If you are trying to experiment with hardware on a table or workbench, you need something plug components into and to hold everything stable. You could use alligator leads and loose stuff laying all over, but if you accidentally yank on a wire it will short or disconnect something, in the worst case blowing up your rPI.

 

Photo 1

 

In Photo 1 above, you can see the overall layout. The DVI computer monitor, USB keyboard and USB mouse are on the left. The square frame with really old style plugboard (that used to use very large old components on little frames) came from an old electronics lab in a school that was being thrown out (lab was probably being turned into a "new media room" or something). 

Onto the old plugboard I bolted on an assortment of new style solderless Breadboard / Proto Board units for inserting leaded parts and DIP ICs to build up circuits. A couple of them have been with me so long they are turning yellow! You can get these at any good hobby / electronic supplier.

An old analog open frame power supply that I scrounged from some equipment that was being thrown out by the same school is bolted to the back. It supplies +5 volts at up to 4 amps (see my posting about using a good beefy power supply), and +12 and -12 at 1 amp. It has a power cord that plugs into the 120 volt wall socket, with the green safety ground tied to the metal frame. There is a hole drilled in the wood to run the power wired underneath. Wiring is very simple, if someone wants a schematic let me know.

Photo 2

 

In photo 2 you can see how I have the rPI bolted to the side so that the monitor, keyboard, mouse and power cables do not move it around. There is a wooden spacer under the inside corner, some insulating foam (just in case, not metal there) and some rubber washers I dug out of my "junk box" to keep trom shorting or damaging the board. The MINI USB power cable goes through a hole on the side under the board.

 Photo 3

 In photo 3 you can see the SPST power switch for the Mini USB going to the Raspberry Pi. This allows me to quickly switch off the rPI without switching off the power supply. Since the PS is analog, it takes a while for the big capacitors in to discharge, and it will run the rPI for quite a few seconds when the plug is pulled out of the wall.

The other switch is a 4 Pole ST switch that allows me to switch off the -12 / +5 / +5 / +12 binding posts with one click, this will be used to power circuitry on the proto boards with jumper wires attached to the binding posts.

You can get toggle switches and binding posts from any good supplier.

 Photo 4

The last photo shows 5 biding posts that have no connection to anything under the board. What I use these for is for connecting test leads from test equipment such as a DVM, Oscilloscope, etc. The leads to them are usually quite heavy, and have relatively thick ends for probing around. I use a banana to banana (or BNC or whatever) lead to connect the equipment, then use a thin long jumper wire to connect to the point in the circuit to be probed. Much less likely to pull something out in the circuit that way.

There is no need to pay someone to cut and strip jumper wires to plug into the proto board, just go dumpster diving and find some pieces of CAT5 solid network cable from an office renovation. Then cut into lengths, strip off the outer sheath, untwist the wires and strip the ends for jumpers.

 To make up the jumpers to plug on the rPI GPIO header, I cut apart an old female DB-25 connector from an old cable (you can find these in good dumpsters everywhere) to get the pins out (hard hacking, but doable if you take care). Then I soldered a jumper cable to an individual pin, covered it in heatshrink, and it's done. You can buy assembled wires with ends, or a fancier breakout cable like this from Adafruit.

I think you will find the time invested in buying a breadboard complete or making one from purchased and scrounged components is well worth the time. It will save you countless hours when your "ratnest" lashup of wires and alligator clips starts to act flaky, or the cat catches a cable and pulls it onto the floor.

Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi to PICAXE via I2C

Two separate programs, one Python program running on the Raspberry Pi and the other in PICAXE basic running on a PICAXE chip and communicating by I2C allow you to use the PICAXE chip as a digital / analog bidirectional I/O expander chip with up to 31 digital/analog I/O pins. So you get a lot more digital input, digital output and analog input pins than you have on the Raspberry Pi alone. As IC2 can support 127 devices, you could support many PICAXES all on different addresses for hundreds of pins of I/O.

You can download the rPI Python and the PICAXE basic code from here. (For some reason, when I tried to paste the code inline in this blog post, it got munged, apparently this is a know issue).

I have wanted to do this for a while, and was thinking about using good old serial but then I decided to see if anyone had done anything similar using I2C. I found this blog post by "AntMan232" which gave me the starting point. Thanks!

I use a PICAXE-40X2 chip which gives up to 31 pins for all kinds of digital and analog I/O, and is a 40 pin DIP package so is easy to work with on a regular proto board. It is available from suppliers in many countries (i.e. PICAXE-40X2 from Canada). The PICAXE is a Microchip PIC microcomputer chip with a special bootloader/OS on it that allows you to develop and download code with the free PICAXE editor.

One could also use the PICAXE ability to do Pulse Width Modulation, control RC servos, drive LCD displays and lots of others, see the PICAXE documentation.

If you have not worked with the PICAXE toolchain, see this older blog post.

Once the rPI has been set up as I2C master and the PICAXE as I2C slave by programming it with the code below, the communications is actually very simple. The rPI Reads/Writes variables into the PICAXE scratch pad where the PICAXE can read and write them. Basically the scratchpad acts as  a bidirectional "window" between the PICAXE program and the rPI Python program. The values are moved back and forth in the background with no further action on the part of the program using the I2C protocol. Very slick!

As the circuit is very simple, I have not drawn a schematic as the hardware setup on the breadboard that I am using is quite simple, but all of the pin to pin connections are shown as a table in the PICAXE source code below.

The PICAXE is powered from rPI 3.3 GPIO pins, draws <10mA. Since rPI can only supply 50 mA, outputs should be buffered. Digital outputs therefore drive 74HC14N buffers to LEDS, powered by a separate 5 volt power supply.  Analog inputs are from a wiper of 10K pot from 3.3V to Ground. Digital inputs are active pullup to 3.3V; sw to Ground. See PICAXE manual for programming cable schematic (don't leave out resistors). Be sure to use lots of capacitor bypassing on your breadboard.



Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi - Why 74HC14N (or other "buffer" Chip)?

** UPDATED Aug 28, 2012**

The reason for putting a buffer chip between the rPI GPIO pin and external electronics is not only convert the 3.3 to 5 volt (or other) logic levels, but protect it from mistakes like applying a high logic level when the chip is configured as an output (some chips are designed to handle this, other are not). Static discharges are also a concern. 

When I mentioned using a 74HC14N to interface to the rPI, reader commented "Amazing that because of these 'new' 3.3v parts we're having to resort to these old 74HCxx parts".

Yes, it IS an old part, but there is a LOT of inertia around 7400 class parts, and a LOT of derivative types like the 74HCXX parts. As this article states "Several generations of pin-compatible descendants of the original family have since become de-facto standard electronic components"

You can get the pinouts and more info for the 74HC14N here. Note that it is a "Hex inverter" which means that it has 6 inverters in the package, and as a bonus it has a Schmitt trigger input, which will tend to clean up slower transitioning signals is you are using them as an input buffer.

The author of the referenced article also stated that there are modern parts that will do the trick, but if you have the old parts hanging around in your junkbox, or you can get them from an eBay seller, then they are fine.

The other issue of course if getting standard DIP parts as so many new components are surface mount , and are difficult or impossible to breadboard with a proto board.

No matter how complex the main chips, unless you have a circuit specifically designed for a project, you always need some "glue chips" to interface things together.

Some of you have worked with Microchip PIC chips which seem quite robust (I have have accidentally drawn a static spark after walking across a dry rug from a screwdriver tip directly to a PIC I/O pin and it continued to work ok). I suspect that the PIC chips have a lot less (relative) complexity than the Broadcom SOC, so I also suspect that the PIC chips have more room to put I/O buffers, protection diodes, etc. which is needed for the type of apps they are used in.  The SOC is normally buried in a phone or tablet so probably brings out more or less the raw gate output, with less protection I imagine. 

So I am working very carefully around the rPI GPIO pins because of that  :-)

 

Reference:  

http://www.petervis.com/Raspberry_PI/Raspberry_Pi_GPIO_Header/Raspberry_Pi_GPIO_Header.html 

http://en.wikipedia.org/wiki/Electrostatic_discharge#Damage_prevention_in_electronics

http://en.wikipedia.org/wiki/7400_series

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2551

http://en.wikipedia.org/wiki/Dual_in-line_package

http://en.wikipedia.org/wiki/Surface_mount


Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry PI – Safely Interfacing to GPIO Pins

I screwed a rPI to an old breadboard I had, and bolted an old open frame analog +5, +/- 12 supply to the back and wired it all up.

In the last post I got a python program toggling all the I/O ports on and off at 1 second interval, will send out the code. At this point just measuring the result with a high impedance logic probe.

Next problem is interfacing the 3.3v rPI levels to the more common 5 v TTL. According to my research:

For 5=>3.3. you can use a simple 10k/20k resistor voltage divider. I have lots of resistors, just have to find them.

For 3.3=>5 This seems to be the cheapest alternative:

     http://www.datasheetcatalog.org/datasheet/philips/74HC14N.pdf

Blowing a $0.50 chip seems to be better than blowing a $35 rPI board :-)

For the next step I want to tie the rPI serial RXD/TXD to the TXD/RSD of a 40 pin PICAXE. Then write a very simple PICAXE program to allow me to use I/O pins on the PICAXE as an "expander" for lots of Digital I/O and Analog in, maybe even use a couple of pins to do PWM, which can be integrated to produce an Analog out. Want to use a simple human readable ascii protocol to marshal data and commands back and forth - http://www.amelek.gda.pl/avr/uisp/srecord.htm

That protocol is really meant for memory mapped data, but you can easily extend it to do commands, could even leave out the checksum.

You could always use a CSV format - http://en.wikipedia.org/wiki/Comma-separated_values - but the srecords would be easier to parse as they are more field oriented.

Probably make it totally polling based to start, i.e. the PICAXE monitors the serial port, the rPI sends data and/or a command, the PICAXE responds and reads and/or outputs the ports, and then the PICAXE sends back any data to the rPI. VERY simple.

Joke is that I once tied together 2 multi $100K ATC simulators using a similar technique (one sim for terminal airspace, the other for precision approach radar) - very simple and easy to test and debug. Nice thing about using a human readable ascii format is that you can hang a dumb terminal (emulator) off the lines to see what is going back and forth for development and debugging (if you slow down the back and forth to human readable speeds :-)

References:

http://www.petervis.com/Raspberry_PI/Raspberry_Pi_GPIO_Header/Raspberry_Pi_GPIO_Header.html

http://code.google.com/p/raspberry-gpio-python/  

http://www.savagecircuits.com/forums/content.php?309-Mixed-Voltage-Systems-Interfacing-5V-and-3-3V-Devices

https://www.google.ca/search?q=interface+3.3v+to+5v&aq=0&oq=interface+3.3+&sugexp=chrome,mod=5&sourceid=chrome&ie=UTF-8

Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi: 8 LED & 8 Button breakout board

I picked up this interesting board from user 9030plc on eBay (visit store here). 

From the eBay description:

"Push your Pi ! 8 LED & 8 Button breakout board for your Raspberry Pi GPIO

Perfect way to learn how to use the GPIO pins.

Plugs into the Raspberry Pi GPIO connector.

Has eight bright green LED's and eight momentary switches.

For a more detailed discription see

     https://projects.drogon.net/more-buttons-and-leds/

For assembly and JAVA programing see

     http://www.savagehomeautomation.com/jj-led 

The normall connector sent mounts directly to the Raspberry Pi.

A box header is available at no charge but you must request it with your order.

Does not include Raspberry Pi or case. Requires assembly."

This would be a very good board for doing some beginner level programming without worrying about shorting things out on a breadboard.

I also found some other useful links concerning the board. Here are the vendors assembly instructions, but the ones above are more detailed. Here is a Python test program, but I find that the above program uses some advanced Python features that newbies may not understand.

Using ideas from it, I created this very simple Python test program that lights a led when the corresponding button is pushed, and should be very clear for the beginner.

Note to run the Python program above on out of the box Raspbian you need to install the module RPIO (which is an "advanced GPIO for the Raspberry Pi. Extends RPi.GPIO with PWM, GPIO interrups, TCP socket interrupts, command line tools and more"):

     $ sudo apt-get install python-setuptools
     $ sudo easy_install -U RPIO

IMHO this is not really a "beginners" soldering kit, you need a fine tip soldering iron (preferably temperature controlled), fine solder, good eyes and a steady hand. Some of the holes are very close and easy to create solder bridges across.

Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi - Connecting Up A Dumb Serial Terminal

 

** Edited Feb 18, 2014 **

A dumb serial terminal (or a PC emulating one) is a handy thing to connect to the rPI for a number of reasons:
 
- when rPI is booted, boot messages are displayed
- you can log in to the rPI from it
- it allows you to connect to and change / debug / update a rPI with no keyboard / monitor that is being used as an embedded controller (perhaps a model B with no Ethernet)
 
Since the rPI uses 3.3 volt logic and a standard PC serial port with a terminal emulator program such as TerraTerm uses the RS232 and ASCII standards, you need to get a converter that converts 3.3 volt levels to RS232.
 
I found this one on eBay from seller skt_flyer:
 

 

If this one is no longer available, there should be lots more, just make sure you get one that works with 3.3 volt power and logic level.

It has pins that connect into my breadboard, you connect the RX, TX, 3.3 volt power and ground to the appropriate pins of the Raspberry Pi. I am not using the CTS/RTS pins for handshaking.

 
From the converter I go thru a null modem cable and then a serial cable to a PC running a terminal emulator program. This is always the fun part about hooking up RS232, you have to worry about the DTE / DCE conventions. 

I have an old laptop that has a real 9 pin PC serial port, if you don't have that you can use a USB to Serial adapter cable.

From the software perspective on the Raspberry Pi, if you have disabled the serial port from spawning a login process you have to enable it again. In the file /etc/inittab on the rPI, if you commented out the line (as I did previously to use the serial port from python):

     #T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

you have to restore it to the original

     T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

This is described more fully in this article (which also discusses how to turn off all the boot messages going to the dumb terminal).

With everything set up like this and the terminal (or terminal emulator software) set for 115200 baud, no handshaking (since CTS/RTS are not used) when the rPI is booted the boot messages will scroll out on the terminal. They you will get a login prompt and can login.

If you are looking for a good Terminal Emulator software for windows, try the open source TerraTerm, which defaults to VT100 emulation.


Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.

Raspberry Pi - GPIO buffer and Webserver Questions

Doug emailed me with some questions:

> These days, embedded control generally means a web page for monitoring and controlling the device.

Well, IMHO the rPI makes this VERY easy, see

http://ve3epp.blogspot.ca/2012/08/raspberry-pi-display-time-on-rpi-web.html


> Need a small board that has a header that plugs directly into the rPi header

Check out this:

http://adafruit.com/products/914

This was mentioned in 

http://ve3epp.blogspot.ca/2012/08/raspberry-pi-home-brew-breadboard.html



> ... buffers for the GPIO lines -- not sure how to address direction.

IMHO Easiest to dedicate lines for out and in. Take a look at this:

http://ve3epp.blogspot.ca/2012/08/raspberry-pi-safely-interfacing-to-gpio.html (first part)

http://ve3epp.blogspot.ca/2012/08/raspberry-pi-why-74hc14n.html

I bought 10 74HC14N off eBay from a cdn supplier for $0.50 each. Looks like he still has some:

http://www.ebay.ca/itm/Lot-2-74HC14N-Hex-Inverter-Schmitt-Trigger-Inputs-7414-QTY-2-/110787294662?pt=LH_DefaultDomain_2&hash=item19cb6ff5c6



> I am thinking seriously of included a dedicated Rs232 interface -- I am a
> big fan of using RS232 for automation interfaciing ( it is reasonable
> robust, and you can always go debugging without a lot of special equipment

Yes, I like good old RS232. If you don't need the full +/-12 volt swing, you can just do a 3.3 to 5 v ttl conversion. See above. Also see:

http://ve3epp.blogspot.ca/2012/08/raspberry-pi-more-about-serial-33v-ttl.html


> I am also interested in 1-wire interface.

Have not done much with this yet, but a lot of people have, see here



You may get the idea that reading some of my old blog posts MAY be useful :-)


Eric Pierce VA3EP - See the Disclaimer in the Introduction

© Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", 1952-2099. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Eric Pierce and "VA3EP Amateur Radio And Other Geek Pursuits", with appropriate and specific direction to the original content.