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by karlkiste
Wed Oct 23, 2013 2:50 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Data diode (unidirectional comm) between 2 RPis
Replies: 28
Views: 12155

Re: Data diode (unidirectional comm) between 2 RPis

Not really. But you might find AND or OR gates which can be used by tying both inputs together.

By the way, hex means "six in one package"

TC7S08F for example is a low pin count gate.
by karlkiste
Wed Oct 23, 2013 2:21 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Data diode (unidirectional comm) between 2 RPis
Replies: 28
Views: 12155

Re: Data diode (unidirectional comm) between 2 RPis

Yes, the schematic is what I had in mind. Just connect all unused inputs to GND or +3v3.

CD4050, HCF4050, HC4050 should all work with 3.3V. HCT4050 will probably not.

74HC125 would be an alternative, 74LS125 not.
by karlkiste
Wed Oct 23, 2013 5:50 am
Forum: Other projects
Topic: Enclosure for sub-zero temperature
Replies: 15
Views: 14666

Re: Enclosure for sub-zero temperature

I think I would use a sealed lead acid battery as long as weight will not be a problem. I'd like to point two things out: In summer, the pi might not want to sit behind 4" styrofoam. Heat is a common problem, cold is not. Just put the pi in the deep freeze and see if it keeps working: I bet it will...
by karlkiste
Wed Oct 23, 2013 5:32 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Data diode (unidirectional comm) between 2 RPis
Replies: 28
Views: 12155

Re: Data diode (unidirectional comm) between 2 RPis

That's the way: TX can only transmit, RX can only receive. This connection, plus GND connection, makes a one-way data link. If you want to really make sure that even if both pis are compromised no data can be sent in the other direction, you'll need a buffer (CD4050 or so) in that TX->RX connection....
by karlkiste
Wed Oct 23, 2013 5:21 am
Forum: Beginners
Topic: powering my model a
Replies: 14
Views: 1690

Re: powering my model a

Go on, seems OK. I'd like to give a little warning on Model A's USB port: I had trouble connecting USB pendrives. They lost connection after some minutes. Plugging a USB hub in between helps, even if it is an unpowered one. Don't know how WIFI works, though. I've recently been powering a Model A lik...
by karlkiste
Wed Oct 23, 2013 5:11 am
Forum: Camera board
Topic: New version of Raspistill
Replies: 150
Views: 29222

Re: New version of Raspistill

poing wrote:So in the control shot when you have pixel that should be gray (127,127,127) but has the values 127,157,127 you enter into the table a value of 0,-30,0 ?
My first idea wouldn't be 0,-30,0 but 1,0.8,1 . Anyone know if it really must be added, not multiplied?
by karlkiste
Tue Oct 22, 2013 10:00 am
Forum: Troubleshooting
Topic: Corrupted SD card
Replies: 4
Views: 1591

Re: Corrupted SD card

I've been doing quite a large project using Pis, and had to use the same lot of SD cards. After lots of trouble, I could only throw a few hundred SD cards to /dev/null and switch to another brand. Half of the SD cards of the "bad" brand had read errors right after first writing to them. Or, they ref...
by karlkiste
Mon Oct 21, 2013 7:21 am
Forum: Graphics, sound and multimedia
Topic: how to run 2 separate video files to 2 lcd screens from 1 pi
Replies: 9
Views: 2578

Re: how to run 2 separate video files to 2 lcd screens from

Nice hardware ! What does it do ? Thanks ;-) It's mostly DC/DC converter, you plug in a 12V 2A power supply, and it powers the pi's with 5V "from the backdoor", i.e. through the power pins on P1. Then, there's a PIC microcontroller which coordinates the videos playing in each pi. The DB9-plug in th...
by karlkiste
Mon Oct 21, 2013 5:16 am
Forum: Graphics, sound and multimedia
Topic: how to run 2 separate video files to 2 lcd screens from 1 pi
Replies: 9
Views: 2578

Re: how to run 2 separate video files to 2 lcd screens from

The short answer: It's impossible. The bold answer: Hide the second pi somewhere, it's small enough. The expensive answer: Combine the two videos to one, and use a HDMI split-screen machine to separate them again. The hand-soldered answer: Combine the two videos, so that one video occupies the odd l...
by karlkiste
Sat Oct 19, 2013 2:04 pm
Forum: Graphics, sound and multimedia
Topic: how to run 2 separate video files to 2 lcd screens from 1 pi
Replies: 9
Views: 2578

Re: how to run 2 separate video files to 2 lcd screens from

My Pi has only a HDMI and a CVBS video output, which can't be enabled at the same time. How do you connect the screens?
by karlkiste
Fri Oct 18, 2013 6:23 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: What is the max clock/baud rates for SPI/I2C/Uart
Replies: 12
Views: 28374

Re: What is the max clock/baud rates for SPI/I2C/Uart

Well, I'm not too close to the hardware either, I let the device drivers do their work... SPI, USB and network can (and probably do) use DMA. The UART can explicitly not use DMA, according to the Broadcom ARM peripherals paper.
by karlkiste
Fri Oct 18, 2013 2:39 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: more tan one power and ground pin nessesery?
Replies: 7
Views: 1440

Re: more tan one power and ground pin nessesery?

You can only draw little current (I think it's rated 50mA) from the 3.3V pins together. That little current can easily go through one pin. I've been powering a Model B pi with camera "backwards" through one 5V and one ground pin from the GPIO header. While this is really not recommended (for bypassi...
by karlkiste
Fri Oct 18, 2013 12:56 pm
Forum: Graphics, sound and multimedia
Topic: Recording audio trough HDMI
Replies: 1
Views: 581

Re: Recording audio trough HDMI

The HDMI-port is output. Also is the RCA video plug and the analog audio port output-only.

GPIO, USB and Network are bi-directional. So if you want to get data of any kind into the pi, you have to use one of these ports.
by karlkiste
Fri Oct 18, 2013 12:51 pm
Forum: Graphics, sound and multimedia
Topic: Espeak sounds slow and broken
Replies: 30
Views: 19813

Re: Espeak sounds slow and broken

No, e-speaking seems to be a speech recognition software, not speech synthesis. espeak's only purpose is to "read text aloud".
by karlkiste
Thu Oct 17, 2013 1:00 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 3.5 TFT hvga module interface
Replies: 23
Views: 9123

Re: 3.5 TFT hvga module interface

I'm not familiar with the general subject, but...
spi0.0 at 250 MHz
That sounds a bit fast to me! I'd start way lower, like 5 or 10 MHz. If all is well, you can rise the data rate, but for debugging slow it down to a safe rate.
by karlkiste
Thu Oct 17, 2013 9:30 am
Forum: Camera board
Topic: Fiddling on memory split with camera enabled
Replies: 2
Views: 752

Re: Fiddling on memory split with camera enabled

Yes, I've set gpu_mem=16 # and 32, 64 I'm still missing 128MB from ARM memory. It's a Model A, so I'd really like to save some bytes there. ----------EDIT------------------- Oooops, sorry! No idea what I did before, now I've tried again, and the split value changes. Sorry for the noise. P.S.: For ru...
by karlkiste
Thu Oct 17, 2013 8:52 am
Forum: Camera board
Topic: Fiddling on memory split with camera enabled
Replies: 2
Views: 752

Fiddling on memory split with camera enabled

Hi! I've just learned that enabling the camera module on raspbian will set the GPU memory to 128MB. I have not found, however, how this is done. Is it hardcoded in start_x.elf? I'd like to try lower values, as I only need the preview function and neither video nor pictures saved or encoded. Maybe ev...
by karlkiste
Wed Oct 16, 2013 7:53 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: UART DMA
Replies: 2
Views: 1466

Re: UART DMA

The "BCM2835 ARM Peripherals" document says on page 175 about the PL011 UART: The following functionality is not supported : ● Infrared Data Association (IrDA) ● Serial InfraRed (SIR) protocol Encoder/Decoder (ENDEC) ● Direct Memory Access (DMA). Therefore, I think you can stop searching a software ...
by karlkiste
Wed Oct 16, 2013 7:35 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: What is the max clock/baud rates for SPI/I2C/Uart
Replies: 12
Views: 28374

Re: What is the max clock/baud rates for SPI/I2C/Uart

Receiving like cat /dev/ttyAMA0 >/file_on_ramdisk I could store data with up to 1 MBaud. At 2 MBaud, data was partly corrupt without any error meaasge. I did not use handshake, which might have helped to get correct data, but which might slow down transmission speed a bit. The data was sent from an ...
by karlkiste
Mon Oct 14, 2013 11:49 am
Forum: Graphics, sound and multimedia
Topic: Can I use a 4.3" LCD with Pi?
Replies: 7
Views: 2353

Re: Can I use a 4.3" LCD with Pi?

Argh... Sorry. Shortcut-posting. You've already found the link I had given again ;-) So, to reduce confusion, I edit this nonsense post.

Greets,
Kiste
by karlkiste
Mon Oct 14, 2013 8:53 am
Forum: Graphics, sound and multimedia
Topic: Can I use a 4.3" LCD with Pi?
Replies: 7
Views: 2353

Re: Can I use a 4.3" LCD with Pi?

The good thing is, you don't need EDID on the pi, you can set a fixed resolution in config.txt. This is most useful when the pi is hard-wired to a certain display. When booting, the kernel sets a framebuffer graphics mode (the pi has no native text modes afaik). X will just use that mode, it will no...
by karlkiste
Thu Sep 05, 2013 4:59 am
Forum: Graphics, sound and multimedia
Topic: USB capture card
Replies: 1
Views: 1284

Re: USB capture card

Most devices today use UVC (USB Video Class), and should therefore work on about any linux system.

To be sure, check here:

http://www.ideasonboard.org/uvc/
by karlkiste
Tue Sep 03, 2013 7:11 am
Forum: Graphics, sound and multimedia
Topic: Real-time playback from microphone is delayed, solutions?
Replies: 5
Views: 3278

Re: Real-time playback from microphone is delayed, solutions

I'm no sound expert, but from my knowledge about computers and electronics I would say: For low-latency realtime effects, input and output must be on a single "device". The same clock source must be used for input and output. This is the only way to ensure that the clocks will not get out of sync. I...
by karlkiste
Mon Sep 02, 2013 12:26 pm
Forum: Graphics, sound and multimedia
Topic: adding a speaker
Replies: 12
Views: 9852

Re: adding a speaker

But it hasn't changed since the first version, so maybe the designer knows more than me? I presume, the problem is - that it works :-) It was never meant to be approved by hifi-freaks who claim to hear a difference between speaker cables made from copper and those made from silver. I think it is a ...
by karlkiste
Sun Sep 01, 2013 5:08 pm
Forum: Graphics, sound and multimedia
Topic: adding a speaker
Replies: 12
Views: 9852

Re: adding a speaker

Though, since the 0 - 3v3 swing of the (PWM) audio is devided down by the potential devider to only 1v p-p, and therefore only go ±0.5v, those diodes won't have much effect. This explanation had made more sense to me, if both the anodes and the cathodes had been connected to GND. Then the swing wou...

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