October
2005, Issue 183
The
Silicon Wallet
CY8C27443-Based
Data Manager
SIX
WILL DO
The
Silicon Wallet is a true System-on-a-Chip (SoC). Actually,
the CY8C27443 microcontroller includes all of the blocks
shown in Figure 2; consequently, the final circuit shown
in Figure 3 has only six parts. Well, to be fair, the
Invention Board was part of the CY3210-MiniProg1 kit,
which included 0.1- and 10-µF bypass capacitors in parallel
to power rails.
|
(Click
here to enlarge)
|
Figure
3—Compare this diagram to Figure 2 to get an idea
of the level of integration possible with the PSoC.
I used the Invention Board to make development easy,
but you can replace it with a bare CY8C27443 and
add a couple of bypass capacitors. In that case,
the component count would jump to an astonishing
eight parts! |
The
circuit is not critical. The only aspect needing a bit
of care is the working point of phototransistor PH1.
If the sensor is too sensitive, ambient light and screen
base luminosity (light is always emitted, especially
by LCD monitors) will disturb it. Conversely, insufficient
sensitivity will make the device unable to function
on all but the brightest screens. I found that a BP103
phototransistor and a 56-kW
resistor work well. Adjust R1 accordingly if you use
a phototransistor other than the specified model.
The
quadrature encoder—a mechanical type manufactured by
ALPS—is the kind of encoder that replaced old potentiometers
in most car stereos. It is a passive part. Its two quadrature
outputs (A and B) can be thought of as a pair of ordinary
switches operated by rotating the shaft. The encoder
also features an additional switch that can be operated
by pushing the shaft. I’ve used the switch for detecting
when the Silicon Wallet is pressed against the PC screen
in order to enter Data Entry mode automatically. Alternatively,
of course, you can use a distinct detector switch. External
pull-ups on these inputs are unnecessary because the
PSoC provides programmable pull-up on its pins.
The
display is a 2 × 16 alphanumeric LCD module based on
the Hitachi HD44780 controller. Connection of pin 3
(contrast control) depends on the module model. Recent
modules, including the MDLS16265BSS I used for the prototype,
require you to connect pin 3 to GND. Different parts
may require you to leave this pin floating, while older
modules may need an external trimmer to adjust the contrast.
The
application doesn’t require precise timing. On the contrary,
it’s designed to adapt to the unpredictable timing tolerances
of web browsers and PCs. Therefore, I saved the cost
of power regulation by disabling the Switch mode pump.
Power comes directly from three 1.5-V batteries with
SW1 operating as power switch.
The
circuit is definitely optimized. Try using a conventional
controller in place of the PSoC, and you’ll be surprised
by the amount of extra parts required!
