Go to advanced search

by joan
Sun Apr 21, 2019 7:19 am
Forum: Beginners
Topic: What transistor to use for PWM of LCD backlight
Replies: 1
Views: 51

Re: What transistor to use for PWM of LCD backlight

Any transistor should cope with those frequencies. You could use the hardware PWM but it would be pretty pointless. Any GPIO would do either via software or hardware timed PWM.
by joan
Fri Apr 19, 2019 10:11 am
Forum: Python
Topic: No SPI Clock
Replies: 3
Views: 73

Re: No SPI Clock

You could enter the following from the command line.

echo "abcdefghijklmnopqrstuvwxyz" >/dev/spidev0.0

I can see the results on a scope.
by joan
Thu Apr 18, 2019 2:28 pm
Forum: Automation, sensing and robotics
Topic: msec timing
Replies: 6
Views: 151

Re: msec timing

You are doing everything right as far as I can tell.

I believe mouse cursor updates now use DMA . pigpio uses DMA to capture the GPIO levels so perhaps the memory bus is getting too congested. I'm afraid I invariably use the Pi headless so it is not something I have experienced.
by joan
Thu Apr 18, 2019 10:15 am
Forum: General discussion
Topic: Control powerfull pwm fans with Pi
Replies: 11
Views: 467

Re: Control powerfull pwm fans with Pi

Don't the fans require a rather odd PWM sequence to start up? I have a memory of proper 4-pin fans not being easily controllable from the Pi.
by joan
Thu Apr 18, 2019 6:42 am
Forum: Automation, sensing and robotics
Topic: msec timing
Replies: 6
Views: 151

Re: msec timing

Can you share some code which shows the problem? Some output which shows the problem would also be useful.
by joan
Wed Apr 17, 2019 1:35 pm
Forum: Automation, sensing and robotics
Topic: msec timing
Replies: 6
Views: 151

Re: msec timing

pigpio will time the difference between two GPIO level changes to the accuracy provided. If by RC you mean Resistance Capacitor timing circuit also see http://abyz.me.uk/rpi/pigpio/examples.h ... pot_cap_py and http://abyz.me.uk/rpi/pigpio/examples.h ... p_charge_c
by joan
Tue Apr 16, 2019 8:44 pm
Forum: Graphics, sound and multimedia
Topic: RPI control WS2812B LEDS with pwm chip
Replies: 3
Views: 87

Re: RPI control WS2812B LEDS with pwm chip

I don't understand how the PCA9685 could be of any use to drive a WS2812B.
by joan
Tue Apr 16, 2019 1:56 pm
Forum: Beginners
Topic: Build/Buy 128 Button Matrix
Replies: 10
Views: 254

Re: Build/Buy 128 Button Matrix

I'd go for the shift registers. I'm playing around with some SN74HC165 at the moment. I have 7 on a breadboard for 56 inputs. It seems quite practical using Python. For the data transfer I'm using the SPI hardware.
sn74hc165-a.jpg
sn74hc165-a.jpg (61.62 KiB) Viewed 215 times
by joan
Mon Apr 15, 2019 2:47 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: I2C address 0x78
Replies: 5
Views: 130

Re: I2C address 0x78

It is silly of them to use a reserved address (it is used to indicate I2C 10-bit addressing). You will probably have to bit bang with software to read the device. As a quickish test you could try http://abyz.me.uk/rpi/pigpio/pigs.html#BI2CO however it assumes you have some knowledge of the I2C proto...
by joan
Sat Apr 13, 2019 6:48 am
Forum: Automation, sensing and robotics
Topic: l298n for 3 motors
Replies: 1
Views: 72

Re: l298n for 3 motors

No, the L298N chip only supports two motors. Buy two or look for a driver board with two.
by joan
Fri Apr 12, 2019 7:43 pm
Forum: General discussion
Topic: what is use of GCIO_GCLK
Replies: 5
Views: 170

Re: what is use of GCIO_GCLK

There are three GPCLKs GPCLK0 which is available on GPIOs 4, 20, 32 and 34 (the latter two only on CM) GPCLK1 which is available on GPIOs 5 and 20 GPCLK2 which is available on GPIO 21 I can't remember if any of them are already used by the Pi's hardware. Details are in the BCM2835 ARM Peripherals d...
by joan
Fri Apr 12, 2019 12:02 pm
Forum: Beginners
Topic: Controlling continuous servo motor on Raspberry Pi 3 B+ w/ Python
Replies: 4
Views: 104

Re: Controlling continuous servo motor on Raspberry Pi 3 B+ w/ Python

Can we have a link to the specs?

Have you connected it to a Raspberry Pi and checked the feedback signal?
by joan
Wed Apr 10, 2019 7:28 am
Forum: Automation, sensing and robotics
Topic: RPi.GPIO can turn a relay on... but not off?!
Replies: 4
Views: 163

Re: RPi.GPIO can turn a relay on... but not off?!

It sounds like you haven't bought a Pi compatible relay module.

It's a bit of a giveaway that it switches on when the GPIO is set to be an output and off when the GPIO is set to be an input. The relay module probably needs 5V GPIO which the Pi does not have.
by joan
Tue Apr 09, 2019 4:55 pm
Forum: Automation, sensing and robotics
Topic: Can L298N power up a Raspberry Pi?
Replies: 3
Views: 133

Re: Can L298N power up a Raspberry Pi?

No it can not. The L298N module power supply is intended to provide enough current for the logic circuitry, not a computer. It supplies enough for an Arduino which is low power device, nowhere near enough for a Pi.
by joan
Mon Apr 08, 2019 7:24 am
Forum: Python
Topic: Measuring frequency via GPIO
Replies: 4
Views: 2352

Re: Measuring frequency via GPIO

@tedder

Thanks, I have now corrected the link.
by joan
Sun Apr 07, 2019 10:41 am
Forum: General discussion
Topic: anemometer - how to 'average' readings
Replies: 17
Views: 451

Re: anemometer - how to 'average' readings

It all seems a bit moot as the input times don't actually reflect the rotation time of the anemometer. Not 100% sure what you mean. In most simple/inexpensive/non-ultrasonic anemometers the number of rotations of the cups is counted, not the time of rotation. The Davis ones for example are designed...
by joan
Sun Apr 07, 2019 9:39 am
Forum: General discussion
Topic: anemometer - how to 'average' readings
Replies: 17
Views: 451

Re: anemometer - how to 'average' readings

It all seems a bit moot as the input times don't actually reflect the rotation time of the anemometer. I'd get that as accurate as possible before smoothing the data.
by joan
Fri Apr 05, 2019 3:04 pm
Forum: Beginners
Topic: Controlling of brightness of Multiple LEDs using PWM on Raspberry Pi
Replies: 2
Views: 87

Re: Controlling of brightness of Multiple LEDs using PWM on Raspberry Pi

Possibly the simplest method is to use my pigpio daemon. http://abyz.me.uk/rpi/pigpio/ It will allow you to generate suitable PWM on all the GPIO on the expansion header. As an experiment you can try the following from the command line. sudo pigpiod # assuming you have GPIO attached to (BCM) GPIO 4....
by joan
Fri Apr 05, 2019 7:58 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: software i2c & 5v slaves
Replies: 4
Views: 216

Re: software i2c & 5v slaves

All the PI GPIO are 3V3 safe only. Make sure any I2C devices you use preferably don't have pull-ups fitted or that they are to 3V3.

Software I2C GPIO are the same as the hardware I2C GPIO as far as you are concerned.
by joan
Thu Apr 04, 2019 10:16 am
Forum: Troubleshooting
Topic: Having trouble with my servos
Replies: 7
Views: 148

Re: Having trouble with my servos

If it's drawing 700mA it's probably stripping or stripped the gears. It should only draw significant current when doing work.
by joan
Thu Apr 04, 2019 8:27 am
Forum: Troubleshooting
Topic: Having trouble with my servos
Replies: 7
Views: 148

Re: Having trouble with my servos

Are you sure the servos support those pulse lengths? Not all servos accept 500µs (2.5%) and 2500µs (12.5%). You might be stripping the servo gears.
by joan
Wed Apr 03, 2019 4:43 pm
Forum: Beginners
Topic: Read digital signal fast
Replies: 2
Views: 118

Re: Read digital signal fast

I will be interested to know how you get on. The pigpio daemon will sample the GPIO at 1MHz if started with the -s 1 option. I don't recommend this sample rate for normal use, there will be jitter. http://abyz.me.uk/rpi/pigpio/pigpiod.html sudo pigpiod -s 1 The monitor GPIO script will then display ...
by joan
Tue Apr 02, 2019 2:38 pm
Forum: C/C++
Topic: why does this error occurs?
Replies: 5
Views: 1397

Re: why does this error occurs?

Are you including the library in the program link stage?

@swampdog pointed out you should include the library.

gcc -lm -o final final.c -lwiringPi
by joan
Tue Apr 02, 2019 11:37 am
Forum: Troubleshooting
Topic: Multiple SDA/SCL | Getting 16x32 RGB LED to work with MCP23017?
Replies: 1
Views: 37

Re: Multiple SDA/SCL | Getting 16x32 RGB LED to work with MCP23017?

All the SDA should be connected together. All the SCL should be connected together. It doesn't matter much how this is achieved, that is a question of the preferred wiring. You could daisy chain from Pi to screen, the screen to MCP. You could have a wire from Pi to screen and Pi to MCP. Personally I...
by joan
Sun Mar 31, 2019 12:20 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: PCF8591 I2C Issues
Replies: 11
Views: 336

Re: PCF8591 I2C Issues

If the others (not all grounded) were on the bus they might interfere with the grounded one as their addresses may be random.

Go to advanced search