BuildingAStripboardExtruderController

HOWTO: Building a stripboard Extruder Controller

Pinouts

Pinouts:

• RA0 is thermistor input
• RB0 is heater element controller
• RB1/2 are network comms (see Stepper module for details)
• RB3 is motor PWM output
• RB4/5 are motor direction controls (one is the inverse of the other)
• RB6 is material-empty sensor input
• RB7 is the chopper wheel input (optional)

Variations

Heating element

The heating element is made from nichrome wire. The correct length must be used to prevent drawing too much current for the power supply to handle or too little current to sufficiently heat the material.

First you must select a suitable power output, in general this should be as high as you can afford in your total energy budget. So for example, if your power supply is rated for 12V@10A and the motors and other parts use 6A at peak, then you have 4A to play with for the heater.

By Ohm's law, V=IR or equivalently R=V/I. So R = 12V / 4A = 3Ω (ohms). So the desired resistance for the nichrome wire is 3Ω.

If you check the specifications for your nichrome wire, it will have a value in ohms/meter at a given temperature. You want the value at around your anticipated working temperature. The resistance drops as the temperature increases. The dropping resistance raises the temperature, which in turn drops the resistance further. Luckily this doesn't go on forever but it leads to fairly inaccurate power consumption if you don't have it right.

Say your wire is rated at 13.4Ω/m at 208C (as mine is). Then to get the desired 3Ω, you need 3Ω / 13.4Ω/m = 0.223m or 22.3 centimeters.

This should be connected with heavy gauge wire and wound around the object to heat (which much be non-conductive or electrically insulated).

How to estimate the resistance at your working temperature if your wire specs only have it for a different temperature

-- Main.SimonMcAuliffe - 03 Feb 2006