04.08 Update

This week I came across this fantastic book *which has been discontinued for a while* titled Inkjet Applications by Matt Gilliland. . It has been quite a good resource in further understanding the systems embedded in the print-head and looking at examples of how to hack it. Below are a few notes from the book that I thought were useful/interesting:

• Each cartridge contains approx 12 million ink droplets which is the equivalent of about 750,000 characters
• The print-head should not touch any media, it's possible to produce legible prints by squirting ink from a distance of 1/2"& under the right conditions the print-head can shoot up to 6"
• The cartridge does not use the two left-most contacts on the flex cable, as they are shorted together - one use is to implement a "loop back" detection circuit to verify whether or not the cable is plugged to the connector
• Each nozzle is completely independent of the others, although a single ink supply feeds all nozzles.
• Since the resistor is heated by current flow - it's important that the voltage pulse and duration is no more than 40 microjoules of energy as to not burn the resistor
• Do not fire more than two droplets at a time. The droplets from the nozzles must also be physically separated from each other. For example, #1 + #7 or #8 + #2
• Wait a total of 800 microseconds before firing the next droplet out of the same nozzle as a minimum for pulse spacing between successive droplets.

We continued to develop the print-head and have switched our FPC connector to the Würth Elektronik connector - which has a 1.0mm pitch, this time around the print flex cable fit well.

We were trying to understand the function of the ULN2803 transistor - it has a total of 18 pin connections, with pins 1 - 8 being the base of each consecutive transistor and pins 11 - 18 being the collector of each consecutive transistor. The ULN2803 chip is used to:

• Control inductive loads - the darlington array act as seperate 8 individual switches that can be turned off and on as desired.
• Drive multiple loads - it is capable of driving 8 loads at a time

We used a simple Arduino code to send electrical pulses to a single nozzle to squirt ink. After a few trial and errors, it worked! :) We had a little fun with free-hand printing.

int outPin = 8; // digital pin 8 void setup() { pinMode(outPin, OUTPUT); // sets the digital pin as output } void loop() { digitalWrite(outPin, HIGH); // sets the pin on delayMicroseconds(5); // pauses for 50 microseconds digitalWrite(outPin, LOW); // sets the pin off delayMicroseconds(1000); // pauses for 50 microseconds }