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PiMSO – A Raspberry Pi based Wi-Fi Oscilloscope


PiMSO, is a Raspberry Pi controlled 200 Msa/S mixed signal oscilloscope. Depending on your application, it can be configure to use the Midori browser on the Pi GUI or access remotely via the internet. Since the PiMSO GUI is web based, You can also control it from a browser on your tablet or smart phone. But what happens when you are at a location that there are no convenient access to a network? For this project I’ll demonstrate how to build a Raspberry Pi based oscilloscope that is also a Wireless Access Point.


As a bare minimum you’ll need the Raspberry Pi and a Ralink RT5370 based Wi-Fi dongle. For this project I used the Tenda W311M from MicroCenter, primarily because it is Access Point capable and inexpensive. An even less expensive dongle that based on the same Ralink RT5370 chip from Comfast can be purchased from Aliexpress for less than $5 inc S/H. A quick search on Aliexpress for RT5370 should yield a few other options. If you don’t have a MSO-28 you can still try it out, the WebMSO28 GUI will run regardless if you have the MSO-28. It’ll just show “NO DSO”.


If you don’t want to roll your own, you can grab a pre-configured Raspian distro from here and skip to Step 6. Otherwise here is how to roll your own on top of your favorite distro.

Step 1: Setting up the Raspberry Pi

1. Grab the latest version of Raspian from Follow the raw images installation instruction provided on this site

2. Boot up the Raspbian and set the it to boot into command line.

Step 2: Package Installation

1. Gain root privilege.
sudo -i

2. Update the package list.

apt-get update

3. Install the necessary packages.

apt-get install git-core build-essential nginx hostapd iw minicom usbmount dnsmasq libfcgi-dev

4. Go to the home directory.

cd / home/pi

5. wiringPi is not necessary if you don’t have PiLCD, but it is nice to have for future I/O control.

git clone git://
cd wiringPi

6. Grab and install the WebMSO-config.git so the Pi will recognize MSO-28 and MSO-19

cd ..
git clone git://
cd WebMSO-config
cp /home/pi/WebMSO-config/74-linkmso.rules /etc/udev/rules.d/.

7. At this point plug the MSO-28 into the Raspberry Pi, you should see it listed under /dev as MSO-28-0.

Step 3: Setting up the web server

1. Edit the nginx default file.

nano /etc/nginx/sites-available/default

Change the nginx default root directory to /var/www

root /var/www;

2. Also add the following block for fcgi port forwarding.

location /fcgi-bin/mso28ctl.fcgi{
include fastcgi_params;

3. Copy the proxy.conf to /etc/nginx

cp proxy.conf /etc/nginx/.

The content of the proxy.conf is shown below.

proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;

4. Check to see if the gzip is enabled in the /etc/nginx/nginx.conf

nano /etc/nginx/nginx.conf

un-comment gzip on;

gzip on;
gzip_disable "msie6";

5. Create the webpage folder

mkdir /var/www

6. Grab and install the WebMSO28fcgi javascripts content

cd /home/pi
git clone git://
cd WebMSO28fcgi
cp -rf * /var/www/.

7. Start the nginx web server.

/etc/init.d/nginx start

At this point nginx should start serving the web page. ifconfig to get your ipv4 address and access it via a browser from a different computer on the same network. pimso pimso

Step 4: Setting up the FCGI server

1. Add execution privilege of the MSO28 fcgi driver in the /var/www/fcgi-bin directory.

chmod +x /var/www/fcgi-bin/mso28ctl.fcgi

2. Create a temporary ram drive for the mso28 fcgi driver to store the captured data.

mkdir /mnt/tmp
mount -t tmpfs -o size=20m tmpfs /mnt/tmp
ln -s /mnt/tmp /var/www/fcgi-bin/tmp

3. Grab and install the spawn-fcgi and mso28ctl.fcgi

cd /home/pi
git clone git://
copy spawn-fcgi-1.6.3.tar.bz2 to /home/pi and unzip the spawn-fcgi
cp mso28fcgi/spawn-fcgi-1.6.3.tar.bz2 .
tar -xvjf spawn-fcgi-1.6.3.tar.bz2

Install the spawn-fcgi

cd spawn-fcgi-1.6.3
make install
cp src/spawn-fcgi /usr/bin/.

Copy the init script from /home/pi/mso28fcgi to /etc/init.d

cp /home/pi/mso28fcgi/spawn-fcgi1 to /etc/init.d/.
chmod +x /etc/init.d/spawn-fcgi1

4. Compile and copy the mso28ctl to /www/var/fcgi-bin

cd mso28fcgi
touch main.c

5. You can test the installing by starting the spawn-fcgi using

/etc/init.d/spawn-fcgi1 start

You should be able to see the blinking indicator next to the ”’Stby”’ above the timing window of the WebMSO28 client page.

If you see No MSO, then your spwan-fcgi is not running.

To stop the spawn-fcgi ”’ctrl-z”’ and kill the process

fuser -k 9000/tcp

6. To auto start spawn-fcgi on boot.

update-rc.d spawn-fcgi1 defaults

To remove spawn-fcgi from auto boot.

update-rc.d -f spawn-fcgi1 remove

At this point server works with ethernet cable.

Step 5: PiMSO Access Point setup

1. Grab WebMSO28AP files from Github.

git clone git://

2. Copy the various conf files to their directories.

cd WebMSO28AP
cp dnsmasq.conf /etc/.
cp hostpad.conf /etc/hostapd/.
cp hosts /etc/.
cp interfaces /etc/network/.

Add DAEMON_CONF=”/etc/hostapd/hostapd.conf” to /etc/default/hostapd

nano /etc/default/hostapd

Look for DAEMON_CONF=””, insert the following


Enable the hostapd and restart dnsmasq

update-rc.d hostapd enable
/etc/init.d/dnsmasq restart

Step 6: Connecting to PiMSO



You should be able to see and connect to the Access Point with the SSID of “WebMSO” with your portable device. Point the brower on your portable device to


you should be able to see the WebMSO28 web client.

If you have a PiLCD, go to Step 7, otherwise you are done.

Step 7: PiLCD Setup


The goal of PiLCD module is provide a convenient way for the user to interact with a headless Raspberry Pi. The PiLCD module consists of a 16×2 LCD display with a rotary encoder switch. Together they provide a way for user to input data and read the results on the display.

One application is for a headless Raspberry Pi with a Wifi dongle to scan, select and connect to nearby Wifi Access Points.

The PiMSO project demonstrates how the PiLCD module can be used to provide a convenient way for the user see the Access Point and URL info of the PiMSO, it will also display current IPV4 address of the Ethernet connection.

1. In addition to wiringPi, you will also need nslookup, which is available in the dnsuitls package.

apt-get install dnsutils

2. Grab and install the PiLCD project from Github

cd /home/Pi
git clone git://
cd /home/pi/PiLCD

3. Copy the LCDinit scrip to init.d

cp /etc/init.d/.
cd /home/pi/wiringPi/examples
make /home/pi/PiLCD/lcd_ip2.c
chmod +x /etc/init.d/

4. you can test PiLCD by typing


You should be able to see the Wifi AP and URL information and Ethernet IPV4 by spinning the knob.

The LCDinit will execute the lcd_ip2 driver from PiLCD directory.
To run the on boot, do the following

update-rc.d defaults

To remove it from boot

update-rc.d -f remove

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