64 September 2016
READER - TO - READER TECHFORUM
I Got The X10 Blues
My X- 10 home automation gear
has been reliable for years but just
recently has become intermittent. Is
there a way to test for what might be
interfering with the operation?
#9161 Malcom Williams
What's The Deal With Ultra Caps?
I am looking to experiment with
“ultra capacitors” as a replacement
for AA batteries. Is this possible to
do and, if so, what kind of capacitors
would be a good place to start?
#9162 Glen Ross
Cassette to MP3
I have a box of cassette audio
tapes that I want to convert to MP3
format. What's the simplest way to
do it? I have a Windows 10 PC and a
Nakamichi CR-2A cassette deck.
#9163 Samantha Costa
I’m retired and re-learning
electronics. I am confused about the
differences between MOSFET and
“regular” transistors. Is there a rule of
thumb as to when/where/why you
would use one over the other?
#9164 Arthur Bergerson
[#6162 - June 2016]
Wi-Fi For The Pi
Could someone please tell me if
the ESP8266.01 module is compatible
with the Raspberry Pi? And/or where
can I find a Wi-Fi and GPS module
There is an instructable on how to
use the ESP8266 with the Raspberry
Pi at www.instructables.com/id/
Connect-an-ESP8266. However, I
don’t recommend that you use it
because it communicates over the
hardware UART. This will result in
an extremely slow 115 kbps Internet
connection, about 1/100th of the
speed of a typical 10 mbps cable
connection. It will also tie up the
UART which is needed for the GPS.
If you have a Raspberry Pi model
3, you do not need to add a Wi-Fi
adapter at all since one is already
built into the board. Use a version
of Raspbian dated March 2016 or
later to avoid driver issues. For older
boards, the simplest solution for Wi-Fi
is to use a small USB adapter. I have
had success with the Edimax EW-
7811Un, available from Amazon and
others for $9. It supports 802 11b/g/n
up to 150 mbps and it’s supported by
any recent version of Raspbian.
GPS is also straightforward.
Most receivers use a simple async
serial port and are pre-configured
to transfer data at 4800 bps, no
parity, eight data bits, one stop bit,
though this can be overridden in
software. Data is transferred using the
NMEA (National Marine Electronics
Association) protocol. Google “GPS
protocol specification” for information
about this text-only protocol made up
of ‘sentences’ that are easily parsed to
get time and location information. If
you are technically adept, you can get
a Ublox NEO-6M or similar 3. 3 volt
serial GPS module for around $15
from eBay or Amazon, and wire it to
the serial port. Using the 26/40 pin
I/O connector port, 3.3V power is on
pin 1, ground on pin 6, Tx on pin 8,
and Rx on pin 10.
A more expensive but beginner-friendly solution is to use an extender
board known as a HAT that requires
no hardware interfacing. One such
HAT is the “Adafruit Ultimate GPS
HAT for the Raspberry Pi,” adafruit.
com product #2324. This board
includes a GPS receiver, internal
antenna, Real Time Clock (RTC), and
a holder for a CR1220 RTC backup
battery. It also has a U.FL connector
for an optional external antenna.
This will only work with an original
or model 2 Pi as changes to the
hardware in the model 3 has made it
incompatible with this HAT, at least
for now. The original Pi and model
2 Pi work fine. This limitation likely
exists with other GPS HATs. If you
have a model 3, make sure the GPS
HAT mfg. specifically claims support
for it before you buy.
[#6164 - June 2016]
PD Race Timer
Does anyone have a
schematic for a pinewood derby
finish line race timer? I would prefer
to build something that doesn’t use a
microcontroller, if at all possible.
#1 When my grandchildren were
into Pinewood Derby racing, I built a
“which came first” circuit (Figure1).
The system has two 12 volt lamps
mounted above the track at the end.
The car that breaks the beam causes
the lamp to light and locks out the
other track. A tie is not possible.
A 12 volt center-tapped
transformer supplies 5 VDC to the
logic and 12 VAC to the lamps. The
logic consists of NAND gates and set-reset flip-flops. When one FF is set, it
energizes a relay that lights the lamp
and simultaneously locks out the
A 38 or 40 kHz IR transmitter is
mounted above the track at the end
and the receiver is mounted under
the track (or vice versa). You may be
able to find a receiver at RadioShack,
eBay, or Amazon. The receiver is 38
kHz but 40 kHz will work fine. I used
reed relays that will work on five volts
but any five volt relay will work. My