Okay, how do you use the GPIO on the Raspberry Pi again? I’m wondering about the whole thing, what is “pull up” and “pull down”? Why is it conspicuously missing from the Raspberry Pi Quick Reaction Game tutorial? What is this “gpiozero” library? Okay, for the answers. So I searched for GPIO Zero, and I found the Raspberry Pi blog post on it. Basically, its name GPIO Zero is inspired by PyGame Zero, the “zero” being added to the name so that the library can be used with a minimum of boilerplate code. And if you read the blog post on it, in fact the creation routines like “Button” is deliberately designed to mask the user from needing to configure whether a GPIO input is “pull up” or “pull down,” instead assuming the common “pull up” by default. As the blog post says, although this is important to know about electronics, it is not necessary if all you want to do is create some simple interactive setup for a classroom activity. So there you go, that’s why mention of “pull up” and “pull down” is conspicuously missing from the Raspberry Pi GPIO quick reaction game. It probably got rewritten after the advent of GPIO Zero, but before that, there may have been an older version that introduced the pull up and pull down concepts.
- Let me state the answer to the question more clearly here, though. “Pull up” means that a transition from 3.3V to 0V is a transition into the “on” state, “pull down” means that a transition from 0V to 3.3V is a transition into the “on” state.
20170304/https://www.raspberrypi.org/documentation/usage/gpio/
20170304/https://www.raspberrypi.org/learning/python-quick-reaction-game/
20170304/https://www.raspberrypi.org/blog/gpio-zero-a-friendly-python-api-for-physical-computing/
20170304/DuckDuckGo raspberry pi gpio pull up pull down
20170304/https://www.raspberrypi.org/forums/viewtopic.php?t=42544&p=343203
20170304/https://www.raspberrypi.org/blog/using-the-gpio/
20170304/https://www.raspberrypi.org/blog/make-your-own-ribbon-cable-with-gert/
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UPDATE 2018-11-25: With pull-up, you’re connecting the button/switch to a constant ground rather than a constant voltage source, hence it is generally safer and less susceptible to RF interference.
Pull-up means that your GPIO input pin is like a connection to a pull-up resistor (resistor to positive voltage source), pull-down means your GPIO input pin is like a pull-down resistor (resistor to ground). So, for current to flow, the connection on the opposite side of a pull-up input should be ground, and for a pull-down input, it should be the positive voltage source 3.3V.
With this explanation, the phrase “pull-up termination” makes perfect sense. You connect a pull-up resistor to the circuit that provides a positive voltage source on the GPIO pin, hence it is “pull-up.” Also, for the
gpiozerolibrary, pull-up is the default configuration for inputs, which is why the quick reaction game didn’t need to configure it.In the case of output pins, however, “pull-up” and “pull-down” are literally true to their meaning like connection to pull-up and pull-down resistors. A pull-up output will supply the positive voltage source when enabled, and a pull-down output will supply a path to ground when enabled.
UPDATE 2019-11-24: Also, to be really technical about the case of input pins, “pull-up” and “pull-down” are also literally true to their meaning, but it takes a bit more effort to explain. CMOS logic gates must never be floating: the gate must either be connected to the positive voltage source or ground. To ensure this is the case with GPIO input buttons that are “floating” when open and conducting when closed, a pull-up or pull-down resistor is also wired up on the gate side of the CMOS logic gate used for the GPIO input. When the GPIO input button is floating, the value of the CMOS logic gate will be asserted to the value of the pull-up/pull-down resistor, but when the GPIO input button is conducting, the pull-up/pull-down resistor value will short to the opposite side of the GPIO input button, and the CMOS logic gate will be asserted to the voltage value on the opposite side of the GPIO input button.
Matter of fact, if you wire up an LED to a pull-up GPIO input, you will see the LED will dimly light, showing that there is still current flowing even after the CMOS logic gate has been switched. Also note that because CMOS logic gates only consume current when switching, we can take advantage of this fact to use a high value pull-up/down resistor and still get the proper voltage across the CMOS logic gate: because so little current flows after a CMOS logic gate has switched, the CMOS logic gate behaves as a very high impedance load, which means most of the voltage drop is across the CMOS logic gate rather than the pull-up/down resistor, so the voltage value at the gate is very nearly the source supply value. The high-value pull-up/down resistor likewise limits the amount of current drawn when the GPIO input button is conducting.
Keep this in mind when working with Raspberry Pi GPIO inputs at the lowest level. When you configure a GPIO input as pull-up, you will get the value “1” when the button is floating and the value “0” when the button is conducting, which is the opposite of what you’d normally expect from a software standpoint.
Also, note that microcontrollers other than the Raspberry Pi may not have built-in pull-up/pull-down resistors. In that case, you must wire up your own pull-up/pull-down resistors when connecting GPIO inputs. A 4.7 K resistor seems to be recommended as a good value to use.
20191124/DuckDuckGo raspberry pi gpio input pull resistance
20191124/http://www.raspberryvi.org/stories/pull-up-and-pull-down-resistors.htmlBUT, please note, the Raspberry Pi’s built-in pull-up resistors are 50 K to 60 K, and up to 65 K for the pull-up resistors only.
20191220/DuckDuckGo raspberry pi internal pull up resistor value
20191220/https://lb.raspberrypi.org/forums/viewtopic.php?t=202568
20191220/https://www.raspberrypi.org/forums/viewtopic.php?p=336915
20191220/https://elinux.org/RPi_Low-level_peripherals
Now, I’m also interested. Is it possible to build an (E)EPROM programmer with an Arduino or a Raspberry Pi? I’m thinking there may be more information on how to do it with an Arduino, so I better include both in my search query for safe measure. Alas, I was wrong. In fact, the information on how to do so with a Raspberry Pi proves to be more readily available on the Internet.
20170304/DuckDuckGo build a eprom programmer raspberry pi arduino
20170304/http://www.instructables.com/id/Raspberry-Pi-Python-EEPROM-Programmer/
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One particularly key and important note that I must make on the Instructable is that the exact wiring depends on the technical specifications sheet. So, you must be sure to find this for your electronics in question should you attempt to use this technique.
- Nevertheless, I consider it highly instrumental that I can just wire up and program a Raspberry Pi should I want to read and write ROM/EEPROM cartridges. Also this accounts easily and gracefully for different sized cartridges, unlike a purpose-built ROM programmer.
Okay, one thing that the Instructable skimps on is the limited GPIO pin count. What if you want to control more GPIO pins than your Raspberry Pi has? Then, I am told that the solution is to use a Port expander.
20170304/DuckDuckGo control more pins than raspberry pi gpio
20170304/http://raspberrypi.stackexchange.com/questions/3452/getting-more-than-26-gpio-pins
20170304/https://en.wikipedia.org/wiki/Port_expander
- “They go by several names, such as “switch”, “hub” or “splitter”, but they all do the same thing.” No they don’t! The electrical implementation of a GPIO port expander is drastically different than that of a Ethernet network switch.
20170304/https://en.wikipedia.org/wiki/EEPROM
20170304/https://en.wikipedia.org/wiki/EPROM
Indeed, it is very easy to build an EEPROM programmer with a Raspberry Pi. Literally, it’s just a direct wire-up between the Raspberry Pi and the EEPROM chip! CMOS 3.3 V the whole way through. But wait, there must be a caveat for programming an EPROM. Indeed, there is. EPROMs require higher-than-normal voltage levels for programming. Of course, very similar to traditional PROMs. So I would need some sort of additional amplifier chip if I wanted to program an EPROM. However, I suspect one of those must be fairly cheap, right? What would one of those be anyways? They are in fact called “level shifters.” And we’re in luck because Wikipedia has sufficient information on these.
20170305/DuckDuckGo raspberry pi amplify gpio pin output
20170305/http://electronics.stackexchange.com/questions/162685/how-to-increase-the-voltage-of-a-digital-signal
20170305/https://en.wikipedia.org/wiki/Logic_level#Logic_voltage_levels
I imagine that ROM programmers must be fairly cheap nowadays. By the way, does Wikipedia have an article on that? Indeed it does, but it is short, poorly written, and has a few spelling, grammatical, and punctuation errors throughout. Well, there you go. I trekked the ground not tredded very often on Wikipedia. As we know, Wikipedia is biased.
20170304/https://en.wikipedia.org/wiki/Programmer_%28hardware%29
Off-topic:
20170305/https://en.wikipedia.org/wiki/Prom
20170305/https://en.wikipedia.org/wiki/Charge_pump
20170305/https://en.wikipedia.org/wiki/1-Wire
Interestingly, you can use a UART to implement a Dallas 1-Wire bus master.
20170305/https://www.maximintegrated.com/en/app-notes/index.mvp/id/214
Single-wire earth return is the way to create a true “one-wire” connection. Principally, Dallas 1-Wire devices require at least two wires, one for power and data, the other for ground.
20170305/https://en.wikipedia.org/wiki/Single_wire_earth_return