How to use interrupts with Python on the Raspberry Pi and RPi. GPIO part 2 Ras. Pi. TVInterrupts are an efficient way for a program to be able to respond immediately to a specific event. In the previous article I explained the basics of using interrupts in RPi. GPIO and gave an example of a simple wait for an event interrupt program. Format the SD card and install Raspbian Wheezy using Noobs or directly httpswww. Update your Raspberry Pi using the script by. In this second article I will introduce threaded callback which opens up a lot of new possibilities. Threaded callback what the heck is that I know it sounds complicated. And it probably is complicated in the C code its written in, but were Pythonites and we dont have to go there. If you remember the previous example program was just a simple wait for port 2. GND when we press the button and then print a message and exit the program. Bus Driver Torrent Full Game here. Apt-Get Install Webiopi' title='Apt-Get Install Webiopi' />So, while it was waiting, the program wasnt doing anything else. The program only had one thread, which means only one thing was being done at once. Python is capable of running more than one thread at once. Its called multi threading. It means that you can go through more than one piece of code simultaneously. This is where we can reap the benefit of interrupts because we can do something else while we wait for our event to happen. Interrupts are an efficient way for a program to be able to respond immediately to a specific event. In the previous article I explained the basics of using. Just like your postman detector allowed you to get on with something else instead of being distracted by waiting for the mail. So that covers the threading part of threaded callback. Whats a callbackWhen an event is detected in the second thread, it communicates this back to the main thread calls back. What we now have in RPi. GPIO is the ability to start a new thread for an interrupt and specify a set of instructions function that will run when the interrupt occurs in the second thread. This is a threaded callback function. This is like your postman detector giving you a list of reminders of things you wanted to do when your delivery arrives AND doing them for you, so you can carry on with what you want to be doing. So What are we going to do now Well keep most of what we did before and add another button and an event detect threaded callback that runs when the new button is pressed, even though we are still waiting for the first button to be pressed. But this time, the new button will connect GPIO port 2. V 3. V3 when pressed. This will allow us to demonstrate a rising edge detection. So well be setting up port 2. Circuit for second interrupt experiment. Later on well have to modify the code to cope with button bounce, but we wont say any more about that just yet. Do you need to update RPi. Flight Simulator 2004 A Century Of Flight Crack. GPIO If you didnt do it for the first example, you will quite likely need to update your RPi. GPIO package. You can check what version of RPi. GPIO you have in the command line withsudo pythonimport RPi. GPIO as GPIOGPIO. VERSIONThis should show you what RPi. GPIO version you have. You need 0. 5. 2a or higher for this example. Apt-Get Install Webiopi' title='Apt-Get Install Webiopi' />You can exit the python environment with CTRLZInstall RPi. GPIO version 0. 5. If you need to, you can install 0. This will update all your Raspbian packages and may take up to an hourUpdate July 2. The best way to get the latest RPi. GPIO currently 0. SD card with the latest NOOBS or Raspbian. This will give you a clean start with the latest version of RPi. GPIO. And now onto the code. Ive put most of the explanation in the code, so that if you use it, you will still have it. Alex Eames http Ras. Pi. tv. import RPi. GPIO as GPIO. GPIO. GPIO. BCM. GPIO 2. One pulled up, the other down. GND when button pressed and 2. V3 3. 3. V. this enables us to demonstrate both rising and falling edge detection. GPIO. setup2. 3, GPIO. IN, pullupdownGPIO. PUDUP. GPIO. setup2. GPIO. IN, pullupdownGPIO. PUDDOWN. now well define the threaded callback function. Rising edge detected on port 2. Make sure you have a button connected so that when pressed. GPIO port 2. 3 pin 1. GND pin 6n. print You will also need a second button connected so that when pressed. GPIO port 2. 4 pin 1. V3 pin 1. rawinputPress Enter when readyn. The GPIO. addeventdetect line below set things up so that. It will happen even while the program is waiting for. GPIO. addeventdetect2. GPIO. RISING, callbackmycallback. Waiting for falling edge on port 2. GPIO. waitforedge2. GPIO. FALLING. print Falling edge detected. Here endeth the second lesson. Keyboard. Interrupt. GPIO. cleanup clean up GPIO on CTRLC exit. GPIO. cleanup clean up GPIO on normal exit. Two ways to get the above code on your Pi. If you are in the command line on your Pi, typenano interrupt. Then click copy to clipboard above and paste into the nano window. Then. CTRLOEnter. CTRLXAlternatively, you can download this directly to your Pi usingwget http raspi. Then you can run it withsudo python interrupt. Whats supposed to happenWhen you run the code it gives you a message Waiting for falling edge on port 2. If you press button 1, it will terminate the program as before and give you a messageFalling edge detected. If, instead of button 1, you press button 2, youll get a messageRising edge detected on port 2. This will occur as many times as you press the button. The program is still waiting for the original falling edge on port 2. Because your second button press is detected in another thread, it doesnt affect the main thread. You may also notice, depending on how cleanly you press the second button, that sometimes you get more than one message for just one button press. This is called switch bounce. Bouncy, bouncy, bouncy. When you press a button switch, the springy contacts may flex and rapidly make and break contact one or more times. This may cause more than one edge detection to trigger, so you may get more than one message for one button press. There is, of course, a way round it, in software. Why didnt this happen before I hear you ask. The answer is simple. Last time the program was simply waiting for a single button press. As soon as that button press was detected, it stopped waiting. So if the switch bounced, it was ignored. The program had already moved on. In our case, it had closed. But, when the event detection is running constantly in another thread, this is not the case and we actually need to slow things down a bit in what is called software debouncing. How to do software debouncing. In order to debounce, we need to be able to measure time intervals. To do that, we use the time module. Near the top of the program we need to add a lineimport time. I add it immediately after the RPi. GPIO import. import RPi. GPIO as GPIO. GPIO. GPIO. BCMThen, also quite near the top of the program we need to set an intial value for the variable timestamp that we will use to measure time intervals timestamp time. I put this after the GPIO. This sets timestamp equal to the time in seconds right now. GPIO. setup2. 3, GPIO. IN, pullupdownGPIO. PUDUP. GPIO. setup2. GPIO. IN, pullupdownGPIO. PUDDOWN. timestamp time. Now we have to change our threaded callback function from. Rising edge detected on port 2. Rising edge detected on port 2. And now, even if you deliberately press the button twice, as long as you do it within 0. You have debounced the switch, by forcing the program to ignore a button press if it occurs less than 0. If you are IDLE Python joke you can get the amended code herewget http raspi. How does this work Now look at the last line of the function. Hotspot Wi. Fi Access Point. When I was thinking of buying Raspberry Pi few months ago, I was also about to buy 3. G routerAP. When I learned what RPi is, and I saw people trying to make AP out of it, I knew where to place my money I know Ive chosen right RPi as AP gives you enormous number of possibilities wireless streaming of cartoons to your tablet when youre in the car. Your wife if you have one already in the same time can watch Desperate Housewives and you can focus on pleasure from driving. I hope youre interested already so lets do it. Note this tutorial assumes that your RPi already detects your Wi. Fi dongle. If you need to install it, please check our other tutorial. Please make sure your Wi. Fi dongle supports AP mode. This tutorial and script was tested with TP LINK WN7. N based on RTL8. 18. CUS chipset. I know there have been many tutorials on how to do this, but I believe there is none that would be a complete guide for total newbie. I had to compile information from few tutorials to set everything right. Lets go step by step and I will try to explain what and why you need to set up. There will be surprise at the end of article so so not miss anything Before well go to WHAT, I will try to explain WHY. What AP needs to be capable of to be AP 1. Inform devices about AP existence Broadcast SSID or at least allow clients to connect. Authenticate client. Assign IP to the client devices. Route packages to the output network and the other way around. In order to handle all of this, RPi needs the following tools hostapd Host Access. Point Daemon will take care of 1. WPA authorization for 2. Lets install these tools. First well take care of configuration of AP daemon and its security we do it in etchostapdhostapd. NOTE If you copy paste hostapd. Arnold. interfacewlan. AP mode. ssidYourAPSSID your AP SSID. Wi. Fi channel used by AP. WPA and WPA2 configuration. MAC address allowdeny list. IEEE 8. 02. 1. 1. AP will broadcast SSID. WPA algorithm used WPA2 in this case. AP password. wpakeymgmtWPA PSK WPA key mangement type. TKIP encription algorithm. CCMP encription algorithm. Hardware configuration. Wi. Fi dongle chipset. Whether IEEE 8. 02. HT is enabled. devicenameRTL8. CU User friendly description of device optional. Realtek Manufacturer name optional. WPS RF Bands a 5. G, b 2. 4. G, g 2. G, ag dual band1. AP modessidYourAPSSID  your AP SSIDchannel1          Wi. Fi channel used by AP WPA and WPA2 configurationmacaddracl0      indicates that you do not use MAC address allowdeny listauthalgs1        indicates algorithm specified by IEEE 8. AP will broadcast SSIDWPA settingswpa2              WPA algorithm used WPA2 in this casewpapassphrasemysecretpassAP passwordwpakeymgmtWPA PSKWPA key mangement typewpapairwiseTKIPencription algorithmrsnpairwiseCCMPencription algorithmHardware configurationdriverrtl. Wi. Fi dongle chipset                      in majority of cases it will be drivernl. Whether IEEE 8. 02. HT is enableddevicenameRTL8. CUUser friendly description of device optionalmanufacturerRealtek  Manufacturer name optionalhwmodeg             WPS RF Bands a 5. G, b 2. 4. G, g 2. G, ag dual bandNow we need to set up etchostapdhostapd. We do it in etcdefaulthostapd. Put the following line there. DAEMONCONFetchostapdhostapd. DAEMONCONFetchostapdhostapd. OK, perfect. Now lets configure the network settings for clients connecting to AP. We do it in etcdhcpdhcpd. DDNS disabled. default lease time 8. IP lease time valid for a day. IP lease time valid for a day. AP Subnet defintion. Range of IP addresses available for clients. DNS IP in my case, my router is workign as DNS. IP. ddns update style none   DDNS disableddefault lease time. IP lease time valid for a daymax lease time. IP lease time valid for a daysubnet. AP Subnet defintion  range. Range of IP addresses available for clients   option domain name servers. DNS IP in my case, my router is workign as DNS  option domain namehome     optional domain name  option routers  1. IPAgain we need to make sure that DHCP server uses this configuration. In etcdefaultisc dhcp server put the following lines. DHCPDCONFetcdhcpdhcpd. INTERFACESwlan. DHCPDCONFetcdhcpdhcpd. INTERFACESwlan. The last line indicates network interface that will be serving DHCP requests. Were almost done. Lets configure wlan. IP adress the same as router IP in dhcpd. We do it in etcnetworkinterfaces. The last line will set routing rules after restart. Lets turn on packet forwarding in etcsysctl. We will configure routing now by executing assuming eth. WAN interface. sudo iptables t nat A POSTROUTING o eth. MASQUERADE. sudo iptables A FORWARD i eth. RELATED,ESTABLISHED j ACCEPT. A FORWARD i wlan. ACCEPT sudo iptables tnat APOSTROUTING oeth. MASQUERADEsudo iptables AFORWARD ieth. RELATED,ESTABLISHED j. ACCEPTsudo iptables AFORWARD iwlan. ACCEPT  and lets save these setting in a file. Because I had bloody RTL8. CUS chipset I had to replace original hostapd with the one prepared for my chipset. In order to start AP on boot run the following commands. We are done Now restart your RPi There is much easier way to do all of this Use our configuration script and have AP set up in 2 minutes If something does not work, please check if there are any duplicate entries in etcnetworkinterfaces if true, remove them and check again. Let me know if something does not work Great articles that helped a lot http www.