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by RaspberryPaul
Mon Jan 13, 2014 9:27 pm
Forum: Beginners
Topic: Input pin voltage tolerances
Replies: 3
Views: 475

Re: Input pin voltage tolerances

I think you'll be safely within the input high/low specifications. Although Broadcom doesn't publish the specs in their datasheet, specs for similar ARM processors are summarized on this page about digital input and output pin voltage levels . Of all the processors listed, the smallest input low lev...
by RaspberryPaul
Tue Aug 06, 2013 1:35 am
Forum: General discussion
Topic: What's the simple and safe way to do a "shutdown" button?
Replies: 60
Views: 61965

Re: What's the simple and safe way to do a "shutdown" button

I noticed nobody has asked, and the title says shutdown - so this is probably a stupid question. but, does this button also boot the device? or does it then have to be disconnected from power, and reconnecting it turns it on? ideally, I'm looking for a power state toggle(or as close to it as possib...
by RaspberryPaul
Tue Aug 06, 2013 1:23 am
Forum: Beginners
Topic: Momntary switch to boot pi?
Replies: 1
Views: 268

Re: Momntary switch to boot pi?

Hey Trev, You can use a small external circuit to power up the RPi with a momentary button press, and also to power it back down with the same button. Take a look at this MOSFET circuit . If you want it to shut down safely (a "soft" shut down), you'll have to install an interrupt service routine on ...
by RaspberryPaul
Tue Aug 06, 2013 1:15 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Electronics basics for novice
Replies: 5
Views: 905

Re: Electronics basics for novice

At our company, Mosaic Industries, we recommend The Art of Electronics to new employees to get them up to speed quickly with basic electronic circuitry. I used to teach from it, and it's very good.
by RaspberryPaul
Wed Jul 31, 2013 2:22 am
Forum: General discussion
Topic: GPIO.FALLING INSANELY! sensitive
Replies: 5
Views: 1078

Re: GPIO.FALLING INSANELY! sensitive

I concur with Mahjong, you should always use a pull-up/down of 10K or less on any input, and if you have a long line or are concerned that there is much RF in the environment, bypass the input pin with a 10nF ceramic capacitor to ground. The internal pull-up/down is rather weak, at 50K as shown in t...
by RaspberryPaul
Wed Jul 31, 2013 2:13 am
Forum: Other projects
Topic: on off switch
Replies: 65
Views: 138803

Re: on off switch

Unfortunately, an ON/OFF switch with a software method for safely powering down the RPi really is needed, and isn't part of the package. Here's a schematic for a good soft power switch . You'll also need a Python script to recognize a GPIO interrupt, shut down processes, then issue a GPIO signal bac...
by RaspberryPaul
Wed Jul 31, 2013 2:07 am
Forum: Beginners
Topic: On/off switch
Replies: 8
Views: 2337

Re: On/off switch

Instead of using an electromechanical relay, a more elegant ON/OFF switch is this two MOSFET circuit. A push of a button turns ON the Raspberry Pi, another short push signals the RPi to turn itself OFF, and a long press can force it OFF.
by RaspberryPaul
Fri Jul 26, 2013 7:18 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Input and Output using one GPIO pin
Replies: 32
Views: 14359

Re: Input and Output using one GPIO pin

You can expand just a few GPIO lines to read many more switch closures, using a switch multiplexing method shown here. So, for example, with just 4 GPIO lines you could read 12 keypad buttons.
by RaspberryPaul
Fri Jul 26, 2013 7:09 am
Forum: Beginners
Topic: electrical specifications
Replies: 7
Views: 919

Re: electrical specifications

Unfortunately the brcm chip doesn't have a real datasheet with I/O pin electrical specifications, so it's hard to know what the GPIO specs really are. But this page on GPIO specs summarizes the specs of similar chips -- the RPi pin specs should be similar.
by RaspberryPaul
Fri Jul 26, 2013 6:59 am
Forum: Add-ons
Topic: Digital Raspberry Pi On/Off Switch
Replies: 3
Views: 4167

Re: Digital Raspberry Pi On/Off Switch

Nice video Callum. You might want to check out this similar toggle circuit that uses only one button, and build up a circuit using it. It gives the Raspberry Pi a chance to turn itself OFF, but if it doesn't you can hold down the button you can force the Raspberry Pi OFF. You can also use MOSFET tra...
by RaspberryPaul
Fri Jul 26, 2013 5:31 am
Forum: Other projects
Topic: Pi on / off PSU relay switch
Replies: 34
Views: 26765

Re: Pi on / off PSU relay switch

As an alternative to using electromechanical relays, this simple MOSFET power ON/OFF circuit works well. With the push of a button it can turn ON the Raspberry Pi, or turn it OFF, or signal the RPi to turn itself OFF.
by RaspberryPaul
Fri Jul 26, 2013 12:23 am
Forum: Advanced users
Topic: Soft Power Button/Switch?
Replies: 14
Views: 12139

Re: Soft Power Button/Switch?

Here's a simple MOSFET circuit for a soft power switch for the RPi. It applies power when you momentarily press a button, with another momentary button press it signals the RPi to shutdown and turn itself off (the RPi needs to read then set one of the GPIO pins), and forces the RPi OFF with a long b...

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