Like the title said, I need more GPIO pins or just a way to control a lot leds
So I need to control more than 40 leds, or even more, anyway more than raspberry pi has GPIO pins. So I know that there is extension board for Raspberry Pi that extends the GPIO, that's one way to solve it. If anyone ever had one can recommend it to me.
Another idea that I got was to use led matrix but instead use the same idea, I mean for example led row 1 and column 4 or so, but the leds won't be in Grid, instead, they will be separated with wires. But the problem, if we want to do like that:
X O X
O X O
X O X
where X is on and O is off, it's not possible. All leds will be lit up, not like in the pattern. If anyone has the solution to one of the ideas then please share it with me, thank you for your time!
You want to control lots of LEDs using as few GPIO pins as possible.
Solution
The way to do this is to use a technique called Charlieplexing. The name comes from the inventor, Charlie Allen of the company Maxim, and the technique takes advantage of the feature of GPIO pins that allows them to be changed from outputs to inputs while a program is running. When a pin is changed to be an input, not enough current will flow through it to light an LED or influence other pins connected to the LED that are set as outputs.
use breadboard
for more information go to this link
http://razzpisampler.oreilly.com/ch04.html
Related
I really wanted at first an rs232 8-channel relay board that I could command devices to turn on/off with a command string.
All of the ones I found online have the same deficiency in functionality for me: you can't set a subset of relays at the exact time. I can set relay 1 on, and then relay 7 on afterwards, I can set all 8 relays at once, but there is no command structure to pick out the exact leds I would like to turn on/off.
In the past I have dealt with hardware that had a bit-map of the IO pins, and a bit-map of the states and would apply all 8 settings at once. here are some examples:
to set pins 1 and 7 to on and the other pins off (8-bit binary bit-mapping,) send the following byte: in binary: 0100 0001b
to set pins 1,2,3,6 to on and the other pins off (8-bit binary bit-mapping,) send the following byte: in binary: 0010 0111b
I couldn't find any such device to do this so I thought I could make one with a raspberry pi using a simple 8-channel relay board, something like this:
https://www.amazon.com/SainSmart-101-70-102-8-Channel-Relay-Module/dp/B0057OC5WK
but on a Raspberry Pi, I'm running into the same issue: I don't see a way to set the gpio pins as a block command, only individually setting them in a for loop. I looked all morning and can see things like gpioctl, and mmio, but I can't put it all together to a simple proof of concept program on a testboard, any help would be appreciated.
I would really like a solution in C or scripting,
Thanks,
jleslie
Is it possible to measure 3 specific resistor values by using GPIO / Without using a full ADC setup?
I have an alarm sensor that I want to hook up to my GPIO. This sensor has 3 specific resistors value, based on it's state:
1) Normal - 4k7
2) Alarm - 9k3
3) Tamper - infinite.
Due to long lines, I would prefer 12V power on one side.
I would like to be able to detect these states by 2 normal GPIO input pins.
Is that even possible? What would be the schematic needed for this?
Or is the only solution to use (external) ADC's?
I am thinking about a voltage diver with resistors and a 1N4148 diode to clip it to 3v3. But so far my results are unfruitfull.
Thanks.
The problem here is you have three levels to measure. If we had two we could use a simple resistor divider setup to make (say) the 4k7 and 9k3 outputs on the sensor to logic 0 (<=0.8V) or logic 1 (>=1.3V) on a single GPIO pin. We could do this on two GPIO pins if we had two "independent samples" of the sensor output rather than one.
Given the above it is possible to design some simple logic network to do the comparisons but as the other comment mentions you're off into the realms of electronics.
ADC is the simplest way to go if you want to stay in the software domain. The are other SBC devices e.g. ESP8266 which have onboard ADC functionality and built-in Wifi https://esp8266-projects.org/2015/03/internal-adc-esp8266/ or you can hook up an add-on ADC to the Rpi for example https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters
Good luck
I'm confused regarding how much current 5LP GPIO pins can drive; any help is appreciated.
Here's where I get confused:
The CY8CKIT-059's "User LED BLUE" is an LTST-C170TBKT from Lite-On
Inc.
This LED has a DC Forward Current of 20 mA, according to its
data sheet.
On the CY8CKIT-059, this LED is driven by a single pin
P2_1 (via a 820 ohm resister), according to the CY8CKIT-059
schematics.
Cypress AN72382, § 2.4 states "In general, [PSOC 5LP]
GPIO pins can source 4 mA."
My confusion: If the PSOC 5LP GPIO pins can only source 4 mA (unless ganged), then how can pin P2_1 drive enough current to light "User LED BLUE" if that LED has a DC Forward Current of 20 mA?
What am I missing here?
I'm sure it is something really obvious.
Thanks in advance,
-Chris
The key distinction is source vs. sink, the pins can source less current than they can sink. Note: The concepts should be considered in terms of conventional current flow (positive to negative.)
Sourcing current involves connecting the I/O pin to VCCIOx (positive). Sinking current involves connecting the I/O pin to GROUND.
When driving a LED we will typically connect the LED to a positive voltage source, then to the I/O pin through a resistor. When we want the LED to turn on, the pin must sink current to ground. The pins can control more current this way.
(Image from CircuitsToday.com)
I am trying to drive EPD(ED060SD1) using STM32F429ZGT, and got datasheet from display vendor. But there is no specific explanation of how to drive EPD display or details of pin.
So I want to know what those pin does.. and any hint how to run this display..
Thank you
ED060SD1 Pin List
The stm32 series of microcontrollers do not support EPD displays directly. I think you would need a EPD controller in between to make it work.
You night be able to generate just the digital inputs, then use an external HV supply from a chip like HV850 and then step it down with inline Zener diodes. I used this approach to make a microflyer based on a piezo speaker!
The HV850 has on/off via digital line and needs +4.2V minimum, max Vout is +/-59V on alternate outputs which is ideal for this purpose.
Simply add a high value resistor on the output side to let it discharge when the panel isn't being driven.
I'd put it in extclk mode and run it at 10Hz to reduce power usage.
Looking for some help to be honest, This is not my area of knoladge atall.
Ive read around the question of powering my Pi with a battery, now I nabbed one of these guys for my phone
http://www.amazon.co.uk/13000mAh-Portable-External-Technology-Motorola-Black/dp/B00BQ5KHJW/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1420826597&sr=1-1-catcorr&keywords=anker+astro+e4
Incase the link dies in the future;
Item model number: AK-79AN13K2-BA
Anker® 2nd Gen Astro E4 13000mAh 2-Port (3A Output) Fast
Max 3A Out
5V Out
Now, from what i've read there have been mixed notes of, don't use batterys, only use this battery, don't do this, don't exeed this magical number ( which was differant each time ). so any help would be grately needed. If i was to power my pi via this thing. im I going to get a poof of smoke and need to replace the poor pi :(
A raspberry Pi is powered via USB, which means that it simply takes the 5V supplied via USB to run. As long as your current source is stable (ie. it doesn't change when you draw current from it), no device will care whether it is a battery or a switching power supply. Now, a bare raspberry Pi B uses less than 2W of power, 2W/5V = 0.4A = 400mA, so if that battery pack lives up to its specification, you are going to be fine. The device is spec'ed to provide 13000mAh, so at a constant current of 400mA, this would last you more than 32 hours.
Now, most people attach something to the raspberry, and that something will also draw power, but just add that power to the calculations above, to see if it's going to work out.