Ronja Twibright Labs

Duty cycle preemphasis test with ping

INFO

Naming convention

We will call the network interface eth0. However, it may be named differently, especially if you have a different operating system than Linux.

Requirements

  • ping
  • Operating system where manual ARP and routing table manipulation can be done
  • Twister or AUI Forte
  • Ronja 10M Metropolis Transmitter which is being tested
Drawing
Postscript / PDF / EPS / BIG png / SVG (Inkscape)

Connect the device

Connect the device to the NIC according to the picture. If it's Twister, power it up.

Setting IP address

Assign an IP address 192.168.1.1 and netmask 255.255.255.0 (Linux: ifconfig eth0 192.168.1.1 netmask 255.255.255.0). Determine and write down the MAC address of the card. (Linux: ifconfig eth0).

Making ARP table entry

Set up permanent ARP table entry for the interface eth0, IP address 192.168.1.2 and MAC address from the paper. (Linux: arp -i eth0 -s 192.168.1.2 MAC_address)

Routing table

If the kernel has not already done it, add a routing table entry for interface eth0 and IP address 192.168.1.2 (Linux: route add 192.168.1.2 eth0)

Gallery[dcc]

Eye test

Note: for Inferno, you have to use B/W CCD camera or night shot camcorder instead of eyes because the light is invisible.

Do ping -s 1472 -f 192.168.1.2 (it means packet payload size 1472 bytes) and break it. Repeat couple of times and look at the transmitter during that:

  • If the LED is shining more during ping -s 1472 -f 192.168.1.2 , then the preemphasis circuit is telling the LED to shine too long (test failed).
  • If the LED is shining less during ping -s 1472 -f 192.168.1.2, then the LED is shining too short time (test failed).
  • If you cannot tell a difference, then the duty cycle preemphasis is set correctly (test passed).
Gallery[164b]

Multimeter test

If the eye test passed and you have a photocell or large area photodiode, connect that to a multimeter set to suitable current range, and place it it over the TX LED and secure by some heavy enough object. Then repeat the same, but instead of eye use the multimeter. The higher current, the more the LED is shining.

An expected information missing here?