Kunawut’s knowledge blog

23Aug

Maximum number of threads per process in Linux?

Linux Server, eqso No Comments

Linux doesn’t have a separate threads per process limit, just a limit on the total number of processes on the system (threads are essentially just processes with a shared address space on Linux) which you can view like this:

cat /proc/sys/kernel/threads-max

The default is the number of memory pages/4. You can increase this like:

echo 100000 > /proc/sys/kernel/threads-max

There is also a limit on the number of processes (an hence threads) that a single user may create, seeulimit/getrlimit for details regarding these limits.

23Aug

SIMPLE INTERFACE CIRCUITS

Sound Interface No Comments

Edited for eQSO, from an article by Peter, G4KQU, with his kind permission.

An interface unit allows one to transmit and receive digital modes using a computer sound card. Conveniently, the interfaces below were designed to operate without an external power supply, so before rushing out and spending a fortune on a commercial interface with features you will probably never need or use, consider building your own! I have included here some simple designs that I have built, tested and which work very well considering their simplicity and economy. These circuits will perform well if you intend to run an Internet gateway using the eQSO or EchoLink software. Parts for these circuits (or complete kits) can be obtained from www.modecomponents.co.uk
Continue reading »

23Aug

Sound Card Packet Interface ver2

Sound Interface No Comments

New and Improved Sound Card Packet Interface ver2
now with CW and tested with PSK31, and APRS
by KD5ZUG

Most of the digital communications used in the amateur bands use some form of tone translation. One tone will represent a high and another tone will represent a low, and by shifting between tones data can be transmitted and received. The data is then fed to a computer program that decodes the data in to understandable language or pictures. Early on the tone decoding was done by a device called a TNC (terminal node controller), which is synonymous with a computer modem used on a wire line or telephone network. In fact the early TNC were modified computer modems. Now that most computers come with very advanced soundcards it is possible to connect your radio directly to your PC without a TNC by using the computers sound card and additional software. The following circuit is a description of the circuit and software needed to make the connections between your computer and your radio. I built this circuit to do APRS (automatic positioning and reporting system) on 144.390 MHz, and most recently have used it for PSK31 on 20 and 40 meters. Please refer to http://www.kc2rlm.info/soundcardpacket for a very good and complete discussion on sound card packet radio.

Please refer to the diagrams for the following procedure.

Place the components on the circuit as shown in the “Parts Layout” diagram. Make sure that the LEDs; capacitor, and transformers are positioned as shown. The primary side of the transformers should be facing the top of the board.
There are enough solider pads for each of the wires coming from the 9 pin serial port computer cable, however only 3 are needed (pin 7 RTS , pin 4 DTR and pin 5 ground).
There are 8 solder pads for terminating the plug that will connect to the radio’s microphone jack. If your radio has fewer pins on the microphone plug then not all of the solder pads need to be used. Be sure and connect the wires sequentially with the microphone plug pin 1 connected to the circuit board pin 1, etc.
You will need to solder jumper wires between the place where the microphone plug cable solders to the circuit board and the solder pads for PTT, radio ground, audio in, and audio ground, which are marked on the circuit board. These jumpers could be different for different radio microphone plugs and cables. Check with your radio’s manual to identify which pins correspond to PTT, ground, audio in and audio ground.
Optionally you can install a chassis mounted microphone jack if you want to be able to use the microphone without having to unplug the sound card interface.
Optionally you can install a jack for headphones. This will allow you to listen to the packets as they are received and also allow you to use the radio for voice communications when not doing packet without having to unplug the sound card interface. Your computer will need to be on for this to work.
Set R5 to its center position.

23Aug

SOUND CARD PACKET RADIO

Sound Interface No Comments

Many of you have heard some of us talking about packet radio. For the “OM’s” they may think “That’s so old, and I tought packet died!” Well, not really. Sure there is other stuff out there that is “better?”, but, packet radio is getting a good makeover, and is a great “last mile” messaging system. Interested? read on…this page is going to give you tips, links, setup and the in’s and out’s of what’s new in packet radio!http://www.patmedia.net/ralphmilnes/soundcardpacket/ .

16Nov