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by rzusman
Fri Feb 08, 2019 11:55 pm
Forum: Troubleshooting
Topic: UART DMX with OLA
Replies: 3
Views: 742

Re: UART DMX with OLA

At this point, you need an oscilloscope.

That’s the easiest way to see what signals are being generated - both to the input of the RS-485 board, and at it’s outputs.
by rzusman
Thu Feb 07, 2019 10:54 pm
Forum: Beginners
Topic: how i make this?
Replies: 2
Views: 188

Re: how i make this?

It's essentially impossible. The failure mode for a Flash cell is power-off data retention of less than 10 years. To read and write a cell until failure (cell won't retain the data between the read and write cycles, which might be an hour or so if you are writing the entire device) would take years,...
by rzusman
Thu Feb 07, 2019 2:59 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Uart Raspberry Pi 3B+ Program
Replies: 1
Views: 679

Re: Uart Raspberry Pi 3B+ Program

Try flushing the input buffer before you transmit the character.
by rzusman
Thu Feb 07, 2019 2:46 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: I2C at 9600 baud?
Replies: 4
Views: 399

Re: I2C at 9600 baud?

You could always bit-whack it at any baud rate you want.
I2C is ugly, but I wrote a bit-whacked interface in assembly language decades ago, so it’s not impossible.
by rzusman
Thu Feb 07, 2019 2:33 am
Forum: Advanced users
Topic: How to connect real car steering wheel to Raspberry Pi?
Replies: 1
Views: 723

Re: How to connect real car steering wheel to Raspberry Pi?

You need something like this device: http://www.ti.com/lit/ds/slis128/slis128.pdf

This chip will do the voltage-shifting and signal buffering for you. You will still need to write some software to interpret and generate the LIN frames.
by rzusman
Sun Jan 13, 2019 4:41 pm
Forum: General programming discussion
Topic: smoother RGBW LED fading
Replies: 5
Views: 1037

Re: smoother RGBW LED fading

I made an PWM LED dimmer for a friend’s art project, using a Silicon Labs processor. The 8-bit PWM looked fine, until the LEDs were very dim, and then the last 8-10 steps or so were very abrupt. When I used the 16-bit PWM, the fades were perfectly smooth, all the way to zero brightness. So, PWM gran...
by rzusman
Sun Jan 06, 2019 12:11 am
Forum: HATs and other add-ons
Topic: battery powered pi, implement real power button?
Replies: 12
Views: 3416

Re: battery powered pi, implement real power button?

You need to re-think your circuit. Having the 5v regulator powered all the time is going to kill your battery. That regulator has something like 5mA or quiescent current. Also, you need to be careful about low-side switching. Once you pull the ground, your device naturally floats to Vcc, since the t...
by rzusman
Fri Jan 04, 2019 12:52 am
Forum: HATs and other add-ons
Topic: battery powered pi, implement real power button?
Replies: 12
Views: 3416

Re: battery powered pi, implement real power button?

Don’t dismiss using a separate micro controller as a supervisor so fast...

You can get a tiny micro for a buck or so, and it can handle all the logic.
by rzusman
Tue Jan 01, 2019 10:53 pm
Forum: HATs and other add-ons
Topic: battery powered pi, implement real power button?
Replies: 12
Views: 3416

Re: battery powered pi, implement real power button?

Here’s what I did for my Compute Module design: I have a Supercap backup power supply that allows graceful shutdown. In your case, this would be your batteries. I use a separate micro controller to monitor the state of the supercap charge. Once they are fully charged, I enable my 3.3v and 5v switchi...
by rzusman
Tue Jan 01, 2019 12:52 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: How to connect 20 stepper motors to Raspberry Pi 3b+ ?
Replies: 2
Views: 837

Re: How to connect 20 stepper motors to Raspberry Pi 3b+ ?

You could use something like this: https://www.pololu.com/product/2971

And then connect the enable pin to a serial-in, parallel out shift register, or a port expander.
by rzusman
Mon Dec 31, 2018 5:50 pm
Forum: Compute Module
Topic: Installing software on CM3
Replies: 8
Views: 1577

Re: Installing software on CM3

Yes the module is able to boot with raspbian lite, but I thought that files (such as git clones) could be put on the compute module over the usb slave port? If you follow the instructions PhilE posted above, you should be able to mount the CM as two volumes. Then (from a Linux host), you can just c...
by rzusman
Wed Dec 26, 2018 8:28 pm
Forum: Compute Module
Topic: Installing software on CM3
Replies: 8
Views: 1577

Re: Installing software on CM3

It does not help me, I have the OS up and running. I just don't know how to install software on it. I want to use pip3 to install opencv. Since there is no internet connection, I am having issues. Wait. Do you mean that the CM is up and running? If so, get a USB-Ethernet converter, or a USB-WiFi do...
by rzusman
Sun Dec 23, 2018 2:20 am
Forum: Compute Module
Topic: RTC time is drifting within one day
Replies: 3
Views: 1512

Re: RTC time is drifting within one day

Frankly, the DS1307 accuracy stinks.

Spend the extra money and get the DS3231, which is temperature compensated, and is guaranteed accurate to a a minute or so/year.

http://www.reuk.co.uk/wordpress/accurat ... to-ds1307/
by rzusman
Tue Nov 27, 2018 2:31 am
Forum: General discussion
Topic: Toggling GPIO pins for pulse width of <100ns
Replies: 35
Views: 1921

Re: Toggling GPIO pins for pulse width of <100ns

Raspbian IS Linux...
by rzusman
Mon Nov 26, 2018 11:23 pm
Forum: General discussion
Topic: Toggling GPIO pins for pulse width of <100ns
Replies: 35
Views: 1921

Re: Toggling GPIO pins for pulse width of <100ns

At a clock speed of 1.4Ghz, that's 100 instructions (more or less). From C, using something like WiringPi, you should easily be able to toggle a pin that quickly. BUT: if you are doing this in Linux, there is a non-zero chance that your pulse will be stretched to some very long duration (10mS or mor...
by rzusman
Mon Nov 26, 2018 12:44 am
Forum: General programming discussion
Topic: Picture frame project, managing files
Replies: 7
Views: 3850

Re: Picture frame project, managing files

What scripting language are you using?
It would be pretty simple to do a brute-force check in Python.
by rzusman
Wed Nov 21, 2018 6:06 pm
Forum: Beginners
Topic: GPIO pulse in nanoseconds
Replies: 7
Views: 1277

Re: GPIO pulse in nanoseconds

Have you ‘scoped the output? That’s the only way to be sure of the pulse rise time, width, and fall time.
by rzusman
Wed Nov 21, 2018 5:44 pm
Forum: Beginners
Topic: GPIO pulse in nanoseconds
Replies: 7
Views: 1277

Re: GPIO pulse in nanoseconds

I’d be willing to bet that it’s impossible to generate a pulse that’s narrower than 3nS with a user-space program on the Pi.
Even at 1.4 GHz, that’s only around 4.2 clocks, and there’s going to be way more cycles than that with the function call overhead.
by rzusman
Sun Nov 18, 2018 9:34 pm
Forum: Advanced users
Topic: Check for crashed program periodically?
Replies: 5
Views: 748

Re: Check for crashed program periodically?

You can create a system service that will re-launch a crashed process automatically.

https://medium.com/@benmorel/creating-a ... 1b5c8b91d6

This won’t fix a hung process - you need a watchdog for that.
by rzusman
Thu Nov 15, 2018 4:27 am
Forum: Compute Module
Topic: Possibility connect compute module directly by solder wire directly to its 'connector'.
Replies: 4
Views: 3089

Re: Possibility connect compute module directly by solder wire directly to its 'connector'.

Your time must be worth more than a socket...

I could solder wires to the CM edge connector, but it would take hours to cut and strip all the wires and solder them. Also, the USB connector probably wouldn’t work with pigtail leads - it needs to be controlled impedance.
by rzusman
Sat Nov 03, 2018 12:16 am
Forum: C/C++
Topic: pthread leak?
Replies: 4
Views: 2089

Re: pthread leak?

Don't use a blocking read. Use something like select with a timeout.

Some discussion here: https://stackoverflow.com/questions/634 ... gracefully
by rzusman
Tue Oct 30, 2018 2:08 am
Forum: C/C++
Topic: What does mtkime with tm_isdst = -1 do during DST transition?
Replies: 1
Views: 1781

What does mtkime with tm_isdst = -1 do during DST transition?

I just found a bug in my code, due to me not explicitly setting tm_isdst to -1 when updating the time using mktime. It took me a long time to detect, since I live in Arizona, and we don’t observe DST. Changing the time update routine to have tm_isdst = -1 seems to fix the time update issue I was hav...
by rzusman
Sat Oct 27, 2018 10:36 pm
Forum: Compute Module
Topic: RS485 Communication with Pi Compute 3L
Replies: 18
Views: 7380

Re: RS485 Communication with Pi Compute 3L

Thanks for the link, and I may experiment with it when I have the time, but I'm not sure it will do what I want. The RTS/CTS lines are controlled by the buffer state, as I understand it, and are not really what I want , which is a TE signal that is the exact width of one byte, including the start an...
by rzusman
Sat Oct 27, 2018 5:34 pm
Forum: Compute Module
Topic: RS485 Communication with Pi Compute 3L
Replies: 18
Views: 7380

Re: RS485 Communication with Pi Compute 3L

I use RS-485 on the CM3L. I am using a low baud rate (9,600), so my timing may not be as critical as yours, but I ended up manually controlling the TE input of the RS-485 driver (Enable TE, send data, disable TE). The only way I was able to do that was to put the driver thread to sleep for 10mS, jus...
by rzusman
Thu Oct 11, 2018 12:59 am
Forum: C/C++
Topic: Valgrind
Replies: 21
Views: 2403

Re: Valgrind

Thanks for the suggestions.
The code is quite complicated - it’s a scheduler for controlling industrial lighting, and it communicates via RS-485 and cellular modems. Maybe 20,000 lines of C.

Anyway, I’ll spend some time trying to figure out what is slowing down valgrind so much when I get a chance.

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