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by btidey
Fri Mar 22, 2013 10:08 am
Forum: Automation, sensing and robotics
Topic: Dual Stepper Motor Controller
Replies: 24
Views: 15256

Re: Dual Stepper Motor Controller

Yes. It is safe providing there are no mistakes made wiring it up. The two GPIO pins are only connected to the ULN inputs and to nothing else.

If you want to be triply sure then put say 2K2 resistors in series between the GPIO pins and the inputs.
by btidey
Fri Mar 22, 2013 12:06 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: simple 12VDC protection
Replies: 10
Views: 1600

Re: simple 12VDC protection

They had the schematic on the link you posted and it looks like the pins are directly wired through to the mega168 controller running at 5V with no external pull ups. This controller does have programmable internal pull ups but they are quite high value > 20K which makes it possible to use resistors...
by btidey
Thu Mar 21, 2013 11:46 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: simple 12VDC protection
Replies: 10
Views: 1600

Re: simple 12VDC protection

According to the spec sheet the logic levels are 5V even though they put the 12V on the connector. That makes sense as the board uses a Mega168 as a controller One should definitely make sure the 12V line goes nowhere near the Pi, but that should be easy to check. As the previous post says the criti...
by btidey
Thu Mar 21, 2013 10:59 pm
Forum: Automation, sensing and robotics
Topic: Dual Stepper Motor Controller
Replies: 24
Views: 15256

Re: Dual Stepper Motor Controller

I've now tried out the even simpler wiring which seems to work fine. It means only the 4 original coil drivers are needed and no extra pull ups.
by btidey
Thu Mar 21, 2013 10:41 pm
Forum: Automation, sensing and robotics
Topic: Dual Stepper Motor Controller
Replies: 24
Views: 15256

Re: Dual Stepper Motor Controller

Not sure what went wrong with the code bracketing there but obviously the lack of indents screws up the python.

Here it is as a file.
by btidey
Thu Mar 21, 2013 10:38 pm
Forum: Automation, sensing and robotics
Topic: Dual Stepper Motor Controller
Replies: 24
Views: 15256

Re: Dual Stepper Motor Controller

[quote="simplesi"]These are the motors (with ULN2003 buffer board/LED indicators) that I've got :) Great links people - ta :) The pdf linked to[url]http://www.philadelphia.edu.jo/academics/kaubaidy/uploads/es-mcinterface.pdf[/url] is a great source of quality info and I'll have to give Page 13 a go ...
by btidey
Thu Mar 21, 2013 10:40 am
Forum: Automation, sensing and robotics
Topic: Dual Stepper Motor Controller
Replies: 24
Views: 15256

Re: Dual Stepper Motor Controller

Check out this thread http://www.raspberrypi.org/phpBB3/viewtopic.php?f=63&t=36894&p=308317&hilit=stepper#p308317 You'll find that you can do 2 wire control for each motor with no fancy circuitry, just the darlington buffers. This is based on the fact that for normal stepping the 4 wire controls are...
by btidey
Mon Mar 18, 2013 9:34 am
Forum: HATs and other add-ons
Topic: Gertboard Connection to Pi (cable twist)
Replies: 17
Views: 7405

Re: Gertboard Connection to Pi (cable twist)

Yes. The change I am thinking about is removing the socket from the underside of the Gertboard v2 and putting a pinned header on top so that a conventional ribbon socket to socket can be used to connect them.
by btidey
Sun Mar 17, 2013 9:52 pm
Forum: HATs and other add-ons
Topic: Gertboard Connection to Pi (cable twist)
Replies: 17
Views: 7405

Re: Gertboard Connection to Pi (cable twist)

I am contemplating swapping the under GPIO socket for a pinned header on top to make it compatible with other ribbon solutions I use and to allow use with a cased Pi with ribbon exit. I am OK with the soldering job; my main concern is with the through hole sizes for fitting a new pinned header as it...
by btidey
Fri Mar 15, 2013 10:30 pm
Forum: HATs and other add-ons
Topic: Maxbotix Ultrasonic Rangefinder - LV-EZ1
Replies: 22
Views: 16377

Re: Maxbotix Ultrasonic Rangefinder - LV-EZ1

Yes, The software side could certainly be improved. I was initially trying out using python as a quick way of getting going. For 3 sensors and 3 GPIO pins you can just connect each one as shown. So all 3 connect to +5V and GND in common. Each GPIO then goes through its own 1K resistor to the trigger...
by btidey
Thu Mar 14, 2013 12:24 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: More than 8 GPIO
Replies: 17
Views: 3009

Re: More than 8 GPIO

You want to switch the transistor hard on so that it is saturated. You first look at the maximum current you want the transistor to switch. If your backlight resistor values are OK then that looks like max is 5V / 560R or about 9mA. Assuming the gain of the transistor is at least 100 then it needs a...
by btidey
Wed Mar 13, 2013 7:46 pm
Forum: HATs and other add-ons
Topic: Maxbotix Ultrasonic Rangefinder - LV-EZ1
Replies: 22
Views: 16377

Re: Maxbotix Ultrasonic Rangefinder - LV-EZ1

Here is a simplistic approach which is certainly not optimum in keeping overall measurement time low but works quite well as the raw readings are fairly consistent anyway. The average function takes MEASURE_COUNT readings and then checks for consistency by making sure that all measurements lie withi...
by btidey
Wed Mar 13, 2013 4:41 pm
Forum: HATs and other add-ons
Topic: Maxbotix Ultrasonic Rangefinder - LV-EZ1
Replies: 22
Views: 16377

Re: Maxbotix Ultrasonic Rangefinder - LV-EZ1

Treating the values in a more sophisticated way to weed out any rogues was also something I wanted to play with. The average of 3 was just borrowed from the original code and I added printing the 3 raw results so I could see what the consistency was like. In general I found it pretty good but you ve...
by btidey
Wed Mar 13, 2013 4:09 pm
Forum: HATs and other add-ons
Topic: Maxbotix Ultrasonic Rangefinder - LV-EZ1
Replies: 22
Views: 16377

Re: Maxbotix Ultrasonic Rangefinder - LV-EZ1

I successfully tried out a single pin version driving the trigger and echo from one GPIO pin. I used a simple resistor network to do a bit of level translation and protect the GPIO pins. The values were chosen to give decent levels based on the trigger input having about a 10K pull to +5V. Attachmen...
by btidey
Wed Mar 13, 2013 11:00 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: More than 8 GPIO
Replies: 17
Views: 3009

Re: More than 8 GPIO

Inputs etc look OK, but the back-light signal via the transistor looks dubious to me. There should be a resistor in the base lead at least to limit the current.
by btidey
Wed Mar 13, 2013 10:43 am
Forum: Automation, sensing and robotics
Topic: Automating button presses on a circuit board
Replies: 12
Views: 2034

Re: Automating button presses on a circuit board

A and F are connected already on your board so you only need to use on of those as the common (GND). You have measured the volts on the other pads when they are in an 'open' state which is good. Now you need to know what current they source when they are connected to the ground. Use your meter in cu...
by btidey
Tue Mar 12, 2013 6:22 pm
Forum: General discussion
Topic: GPIO to control stepper motors and switch.
Replies: 10
Views: 3761

Re: GPIO to control stepper motors and switch.

Also if you are controlling the stepper in the normal 4 step sequence then the 4 drive signals are actually in two pairs so 2 that GPIO pins per motor is sufficient (rather than 4) providing one can invert the signals. Coil 1 = GPIO-A Coil 2 = Not GPIO-A Coil 3 = GPIO-B Coil 4 = Not GPIO-B If you ar...
by btidey
Sun Mar 10, 2013 1:19 pm
Forum: HATs and other add-ons
Topic: Maxbotix Ultrasonic Rangefinder - LV-EZ1
Replies: 22
Views: 16377

Re: Maxbotix Ultrasonic Rangefinder - LV-EZ1

Although serial maybe the best way to go with this sensor, it is possible to get good results with Python using PWM as I found from this link. http://www.raspberrypi-spy.co.uk/2013/01/ultrasonic-distance-measurement-using-python-part-2/ This actually used a different type of ultrasonic sensor that o...
by btidey
Sat Mar 02, 2013 7:18 pm
Forum: Automation, sensing and robotics
Topic: Measuring home power consumption using Pi
Replies: 5
Views: 28895

Re: Measuring home power consumption using Pi

If you are monitoring the energy consumption for the whole house then the basic sensor is a clip on current transformer which clamps over the incoming live cable and gives an ac low voltage output across a resistor proportional to the current being consumed. This then has to be input in some way to ...
by btidey
Fri Mar 01, 2013 12:40 pm
Forum: General discussion
Topic: RS232 to Composite
Replies: 2
Views: 951

Re: RS232 to Composite

This should be very easy to do. You can make a connection either to the GPIO serial pins via a RS232 to TTL (3.3V) converter lead. Search eBay, they are pretty cheap. Alternatively you could plug a USB to RS232 converter into one of the USB ports. Software will depend on whether the terminal needs a...
by btidey
Sat Feb 23, 2013 7:02 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Digital POT Driving a LED with SPI
Replies: 4
Views: 2544

Re: Digital POT Driving a LED with SPI

I think the basic logic of the wiring is OK, but when I look at the data sheet the maximum wiper current is supposed to be 1mA which means driving the LED directly is going to be very limited. You would need an analog buffer between the chip and the LED if you wanted to get a decent amount of LED cu...
by btidey
Sat Feb 23, 2013 6:23 pm
Forum: Automation, sensing and robotics
Topic: Detecting mains on/off
Replies: 8
Views: 1515

Re: Detecting mains on/off

If it is just for temporary use then maybe put a small normal mains lamp on each circuit pointed at a LDR.

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