A Program to Control SMD
Soldering Using a Toaster Oven
Ever want to try SMD (surface-mount
device) soldering without using a
magnifying glass and super steady
hands? Production houses use ovens which
cost thousands, but it’s possible to do a
reasonable job with a regular toaster oven.
You just need to control it correctly. Enter the
SparkFun Electronics Reflow Toaster Controller.
by Kit Ryan
This controller looked like a great project for experimenting
with reflow soldering SMD devices at home, but it came
with only rudimentary software. As a learning project,
it had many features to explore, including a PIC16F88 MPU,
thermocouple temperature sensor using the A/D converter,
control buttons for inputs, an LCD readout, and a serial port
with boot loader for quick program changes. A personal goal
was to get back to low level (near assembly code) programming
after decades of being out of touch. Many months and 1,500
lines of C code later, this little controller can really do a lot,
including programmed modes and data logging to your PC.
The controller hardware kit is a snap to build — well
packaged components and no SMDs (!). It even includes a
power supply. All you need is a serial cable to hook it up to
your PC for programming as shown in Figure 1. A feature
of this kit is that the PIC16F88 already comes loaded with
a boot loader so a real programmer isn’t immediately
needed — but more on that later. The kit powers up with
the LED flashing and the LCD readout showing “Spark
Fun.” Very reassuring that everything works.
The circuit, shown in the schematic in Figure 2, is
designed to control a relay that can switch 120 VAC for
regulating the temperature of an ordinary toaster oven.
How it works is that the thermocouple output is amplified
and linearized by the Analog Devices AD849 IC to within
±2 degrees F. No adjustment is needed and I found it to
be within one degree of the reading compared to room
1) This project involves line voltage
connections which are potentially
fatal if mishandled. Double-check all
wires before applying line voltages.
2) Using the Controller for reflow
soldering can result in operating a
toaster oven at extremely high
temperatures, which can burn
fingers or cause fires.
3) Solder materials, whether lead-
based or lead-free, can be toxic if
ingested. The toaster oven you
use for this project should be
permanently dedicated to electronics
and no longer used for heating food
PLEASE USE CAUTION WHEN
OPERATING THIS CONTROLLER.
FIGURE 1. Completed controller project.
June 2008 67