December 2014, AV writes:
"I am very impressed with your
credentials and interests. I began using my EL5500III again after about
twenty years. It's amazing how much of the programming I still
remember. While looking for a manual online, I luckily came upon your
site. Incredible. I might even try to build your analog upload system.
I use my Sharp to program CNC
machines, mostly WEDM (wire electrical discharge machining) in shops
where there is an absence of CAD assistance. I never had a way to back
up. I sold one of my first programs to a guy working on space shuttle
parts or something for Moog back in '86 in Pinellas Park Florida. I
think I got around $75.00 for it.
Anyways, Great site!"
This page documents calculators that "Do Something More!" or are
special in some way. Currently, HP-20S, Sharp EL-5500III,
HP-20S: Installing ROM Programs into RAM
HP-20S has many functions pre-associated with key strokes on the
keyboard. There are also four programs that you can download from
internal ROM memory into the calculators RAM memory. You can view
a quick documentation here on the web page, or download a ROM spreadsheet that
programs. The spreadsheet is much more detailed. The four
In case you forget how to quickly access and use the ROM programs, you
can download a ROM Cheat
to carry with
Sharp EL-5500II EL5500III: Modem
The Sharp EL-5500II and Sharp EL-5500III handheld
calculators came from on era when people used the
TRS-80 computers programmed in BASIC, and the HP-41 and TI-83
introduced programmability into the calculator market.
The EL-5500s combined a standard calculator on the right side of the
keypad with a QWERTY-like keypad for using a BASIC interpretter
programmed into the calculator. Rather than writing cryptic
pneumonic programs with a TI or HP calculator, you could program
directly in the BASIC lanuage.
True to other computers of the time, programs were saved on audio
cassette tape output of the EL-5500iii.
Use the BASIC
command line CSAVE or "CS." for short.
The computer has no battery backup when you replace the main two
be sure to save all your BASIC programs before changing
batteries. That said, you won't be changing batteries that
often. The two CR2032 batteries last between 10 and 20
years. Buying a pack of 10 CR2032 batteries cost me a whopping $2.19
on eBay. I think that works out to about 75 years of
Audio output of the modem is a square wave output, with modem
4000 Hz and 2000 Hz. Bit time is about 2 millseconds and signal is 4
With the LLIST or "LL." command, the Sharp computer will send programs
out the port without modulation. Originally, this function was
designed to print onto their printer. I suspect it's
ASCII-like and for greater compatibility should be inverted to ±12
volts to match RS-232. I have more work to do in order to
document this in detail.
With LLIST there is some handshaking involved. In order to get
the EL-5500III to send data, you have to hold one of the inputs
high. That's what I was doing with the 10 Kohm resister in the
Saving EL-5500 BASIC programs with MP3 backup on your desktop
The modulated audio waveform was meant to record data or programs on a
cassette tape back in
late 1980s. Thirty years later, it seemed appropriate to see if I
could record the audio on my laptop computer and save programs as mp3
or wav files.
Below is a picture of the setup I used. The ancient laptop peeking over
the top of the Macbook is not used. It is sitting on top of my HF
band amateur radio receiver. On the left is a Fluke 97 digital
scope. Next the Macbook, then a perfboard electrical prototyping
board, then the EL-5500. Notice the audio wire from the perfboard
wraps around behind the Macbook laptop and plugs into the audio port of
the laptop. The o'scope wires go behind the laptop and come out
to the perfboard area.
Zooming in closer you can see the green ground wire plugged into the
3rd hole from the top. It appears Sharp is sort of like the old
U.S. Navy electronics courses. They recognize that electricity is
really made up from negatively charged electrons, so when you read
documentation on this 11-pin interface, remember "GND" (pin 2) is at 5
volts and "Vcc" (pin 3) is ground. The cassette tape audio output
is on the
7th hole from the top. I routed the audio across a 10 kohm
resistor potentiometer with a center tap for a volume adjust. The
Sharp has no trouble with a 10 kohm load, and the laptop audio standard
has a high input impedance so it also doesn't load the circuit.
Turns out a volume of about 1/3 scale worked fine.
The two wires from the potentiometer to the laptop computer needed to
convert to a 1/8 phone plug. I had an extra stereo headset wire
left over. Wow! Those wires are really small shielded
cables. The connections were so fragile I got out a glue gun and
added a cardboard splint on the connection.
The Macbook needed to be told to use it's audio port as an input rather
than a headset output. Use the sound option in the System
Preferences app as shown below. Your computer may not have the
Soundflower entries. Soundflower is a separate program I found
that lets me route audio from any application to any other application,
but it's not used to record the EL-5500 cassette audio.
You can use Quicktime to record the audio, but I prefer to use
Audacity, which is kind of like GIMP for audio files. I entered
the EL-5500 and below the audio that was recorded. The part shown
is where the lead-in 4000 Hz carrier is first modulated with
the 2000 Hz bit times. I think the 2000 Hz bits have to be some
sort of a start or sync-bit, but I haven't figured out yet exactly what
digital encoding is used.
On the above picture you can see only a tiny piece of the full
audio. You can download the full audio here (160
KB mp3 1.7
Be ready for a long screeching lead in tone, and then a very quick
burst of modulation at the end that represents the program below.
The modulated part is very short because the program is only 5 lines
Here is the BASIC program that was saved out the cassette audio port
with the CSAVE command, so the audio file is actually a rendition of
this program. Now I need to figure out a way to play this audio
file back to the calculator so I can reload programs and data onto it.
10 INPUT A
20 FOR I=A TO 0 STEP -1
30 PAUSE I
40 NEXT I
50 BEEP A
Remember, this calculator is a fully functional BASIC interpreter is
running on a 1980s
era handheld calculator, running on two little batteries that last for years.
This makes me think of all sorts of remote automation ideas. This
could be a supervisory computer that monitor mechanical health and
welfare of a remote cottage or machine or radio station or
whatnot. Because it needs no external power for at least months,
it can monitor the health of other, more capable, control systems that
need power and are liable to malfunction with power loss.
The problem with this calculator is that when
batteries are changed, you
loose all the memory on the calculator. Now I have a way of
programs and memory variables to my desktop in the form of audio
files. Kind of cool!
The next project is to write an "audio compiler" that can take a BASIC
program from other sources and modulate it into a wav file, which can
then be uploaded to the Sharp EL-5500. If you want to collaborate on making this happen, please contact me.
- HP-20S on Wikipedia
- EL-5500 on
skeleton of this document was originally created using AbiWord
under a Gnome desktop. It was subsequently edited by Konquerer to
become the web page you are reading. Created March 2013. Last
updated May 2013.