is a tiny digital voice playback device that is designed to announce your
personal ham call letters every few minutes. Its small size is perfect for
mounting on video equipped R/C model aircraft.
In the USA, R/C wireless
video hobbyists are required to operate their video transmitters under the
FCC Part 97 regulations (amateur radio). The only exceptions
are the Part 15 approved systems, but these low power alternatives are rarely
used. Other countries have similar requirements. Playing by the rules will
certainly prevent conflicts with government officials, since they can levy
substantial penalties to offenders. But more importantly, following the rules
is the basis of good amateur radio manners.
One of the requirements
that is easily overlooked is the need to identify your station during your
video communications. From what I have seen, some R/C wireless video users
are neglecting to broadcast their ham radio call sign. Essentially, USA hams
must do so every ten minutes and at the end of their communication. Here
is a excerpt from the FCC Part 97 document:
(a) Each amateur station, except a space station or telecommand station,
must transmit its assigned call sign on its transmitting channel at the end
of each communication, and at least every ten minutes during a communication,
for the purpose of clearly making the source of the transmissions from the
station known to those receiving the transmissions. No station may transmit
unidentified communications or signals, or transmit as the station call sign,
any call sign not authorized to the station.
Speak no Evil
I had been using simple
minded methods to identify my video station. My favorite was to point the
camera at a flight box mounted placard that had my call sign printed on it.
Sometimes I merely spoke my call letters into the video systems's microphone.
Both methods worked, but I was often forgetting to land my R/C model aircraft
every ten minutes to do these cheap tricks.
Of course there are
commercially made automatic call sign annunciators. I thought about using
display (OSD) board. These gadgets will electronically overlay
your call sign (or any other text) on the camera's video feed at timed
intervals. However, I was not excited about their size, current requirements,
and cost. The audio based versions that I found were designed for ham shack
use, so size was a problem with them.
As a devote hacker,
I decided to build my own digital voice based call sign annunciator. The
result is HamCam-ID'er. It is small, low power, and provides automatic
call sign announcement over your video transmitter's audio subcarrier. It
automatically mutes your microphone (if used) so that the call sign announcement
can be clearly heard. Material cost is under $20.
Digital is Sometimes
A few years ago I designed
a consumer product that needed to speak a message. The best sounding single
chip voice technology at the time was offered by
Storage Devices (Winbond). Even though that was awhile ago, this firm
continues to take the prize for good audio quality at low cost. The only
thing that has changed is the owners (competitor bought them in a
big-fish-eats-little-fish sort of transaction).
The funny thing about
their "digital" voice chips is that they are not digital at all. Instead,
the ISD folks discovered a way to store analog information (voltage samples)
in a silicon memory array. The stored analog data is retained even when power
is lost, so their audio chips make great play-only devices (but they are
recordable too). Their chips are very integrated and require only a handful
of cheap parts to create voice enabled toys and appliances.
To simplify the project,
I started with a ready-to-use Recording Module from
This $9.95 part (p/n
276-1323) appears to be based on the recently discontinued
IC. This low cost bare-board module offers twenty seconds of recordable sound.
It is a fun gadget and is ready to use after installing a 9V battery. The
photo on the left shows what you get for your $10. Of course we will need
to hack it a bit.
PIC Your Parts
The Radio Shack Recording
Module has a speaker/mic and a couple of push button switches. To use it
in our automatic ID application all we have to do is connect the speaker
leads to our video transmitter's audio input and figure a way to "press"
the play button every ten minutes. Sounds easy, doesn't it? Well it is, sort
of. But we do have to add some parts to complete the job.
The general idea is
to wait ten minutes then trigger the ISD's play mode. I could have used some
"555" timer IC's to get the basic functionality I needed. But I also wanted
to mute the mic and detect the end of message signal. A pushbutton switch
for manually sending the ID at the start and end of the communication was
needed. A status LED seemed like a good idea too. After penciling some design
ideas I decided to reduce the parts count by incorporating a tiny 8-Pin
The chosen microcontroller
is from the vast offerings of
Technology. Actually, your exact PIC choices have some flexibility. You
can use a PIC12C508, PIC12C508A, PIC12C509, and PIC12C509A. Project Update:
You can also use the easier to find PIC12F508 or PIC12F509 instead.
The PIC12C50x is not
a "Flash" part, so you will need a traditional PIC chip programmer to "burn"
the hex file's object code into the microcontroller. Be sure to select the
configuration fuses during chip burning as follows (these are optional settings
within your chip programmer's menus):
By the way, after you
program the PIC it will fail the verify cycle. Do not be alarmed -- everything
is OK. Just ignore the "failure." Whatever you do, do NOT program the chip
If you have trouble
burning the PIC, then please check your programmer. Whatever the fault, it
is not a CamMan hex file issue. The most common problem is that the
user has forgotten to burn the PIC's four config fuses, as shown above. More
programming information can be found starting
The only other active
component is an 8-Pin OpAmp IC. It is used to condition the speaker output
from the ISD module (differential to single ended conversion). It also provides
1V style line level amplification for an electret condenser microphone.
Although you may already have a microphone on your video transmitter, you
will need to use the one from HamCam-ID'er if you wish to retain the mic
Although there are
only two tiny IC's, there are several other passive parts (caps and resistors).
This project is best tackled by an experienced electronic technician. If
you have successfully built any of the other RC-CAM
Electronics Projects then you
should have no problem with this one. Entry level technicians should plan
on getting some hands-on help.
The finished device
is a power miser. It will nominally draw under 3mA. During playback, the
current is 23mA. Eliminating the LED1 lamp will reduce that amount to about
15mA. The allowed voltage range is from 4.5VDC to 12VDC, so it should be
compatible with all R/C wireless video transmitters that have an audio
Stop, Look, and Listen
Before you do ANYTHING,
you must spend some quality time with Radio Shack's ISD voice module. Now
is the time to attach a 9V battery to the board and record your call sign
announcement. If you wait until later you will be very sorry (because you
are going to hack the heck out of the ISD board).
You have up to twenty
seconds for your recorded message, but you do not need to use it all if you
don't want to. I suggest that you cup your hands around the Mic/Speaker
during record and playback to improve audio performance. If you don't
do this the sound level will be too low for good clarity. Practice a few
times to get a feel for what sounds best (good volume, clear voice quality).
Here is a sample of
what a ham ATV operator on 2.4Ghz might want to say:
" This is station Z Z 5 D U K . That is
Zulu-Zulu-Five-Delta-Uniform-Kilo. Experimental ham ATV station operating
on thirteen centimeters. "
Once you get your award
winning announcement recorded you may proceed. So, if you are ready then
let's get the soldering iron warmed up.
The voice module will need to have some parts pruned from it. Franky,
everything that dangles needs to be removed. Use a temperature controlled
soldering iron (700° F) and carefully emancipate the speaker, battery
clip, and record button. The play button is no longer needed, but I left
it on the board.
When you are done with
your pruning you will have some interesting spare parts. Keep them in a safe
place! You never know -- you may need to record a new announcement one day
(not a welcome situation, if you know what I mean).
The control board can
be built using nearly any technique you wish. I needed it to fit inside the
PacTec box used in RC-CAM4, so
size was not a big issue (the enclosure is roomy). A piece of phenolic
perfboard was cut to the same dimensions as the ISD module (1.75" x .95").
My method resulted in double-decker "daughter board" arrangement. Smaller
dimensions are possible.
control board was point-to-point wired using the component leads and 30 AWG
insulated Kynar wire. This wire is normally used for wirewrapping,
but works fine with a soldering iron. I recommend a temperature controlled
iron (700° tip).
Layout is not critical.
I used sockets for the IC's (the empty one is for the PIC). For convenience,
several resistors are mounted on the bottom side on my board. I suggest 1/8
watt resistors to keep things compact.
The schematic's J1,
J2, and J4 components represent the connection points to the ISD voice module.
The J3 connections go to the video transmitter's audio input. There
is no need to add connectors to these areas -- direct wiring is
Connect the custom
control board to the ISD module as follows:
|ISD Speaker Top Pad
|ISD Speaker Bottom Pad
|ISD R3 Top Pad
|End Of Msg Sig
|ISD LED Right Pad
|5V LDO V-Reg
|ISD R3 Bottom Pad
|ISD C1 Neg Pad
|ISD BAT+ Input
|ISD Gnd Input
Check your work carefully.
Do NOT install the PIC chip until you have verified that U2 pin 8 is ground
and the pin 1 has 4.5 to 5.25 VDC on it when a battery is connected. Remove
the battery BEFORE you install the chip. Simple mistakes can destroy electronic
parts and may generally ruin your day.
The audio output from
the control board (J3) is a 1V type line level. It will directly connect
to any video transmitter that has a line level conditioned audio channel
(a common feature). If your transmitter has a built-in microphone then you
must remove it and connect its wires to the board. However, in this situation
you MUST attenuate the signal. The schematic shows an optional L-Pad circuit
that you should use to reduce the line level signal to the mic input's millivolt
level. Resistor R16 can be adjusted if you need to change the volume
(higher value = louder audio).
Here are the audio
connections to route the control board's audio signal to the video
|Line Level Audio
|Tx Audio Line-In / Mic-In
|Tx Audio Gnd (optional)
Testing, 1, 2, 3.
Now its time to test
your work. This is a wise thing to do before you mount the ISD module and
its companion controller board in the enclosure. Here are the necessary test
steps (if any step fails then stop and troubleshoot before proceeding):
Connect the battery.
The LED will blink one time (on, then off) the moment powered is applied.
If you do not see the LED blink once then something is wrong.
Turn on your video
system. Ensure that all A/V cables are connected. Verify that video is
Speak into the microphone.
You should hear your voice on your receiver's speaker.
Press the S1 play button
on the controller board (not the one on the ISD board). The controller's
LED1 announce indicator should turn on and you should hear your recorded
message on the receiver.
The LED should turn
off at the end of your recorded announcement. If it stays on for a full twenty
seconds then something is wrong. It should turn off at the same time
your recorded message ends.
Press the S1 play switch
again. While your digital voice is playing, tap or speak into the microphone
and verify that it is disabled. At the end of playback the mic should function
Wait exactly ten minutes
from the time you pressed the S1 switch. Your recorded voice should play
automatically. It will repeat at ten minute intervals.
Let's Wrap it up
Now you can install
HamCam-ID'er in your enclosure. Mine shared space with my Panasonic board
camera (see RC-CAM4). I used some
double sided tape to join the controller board to the ISD module. Because
of the harsh R/C model environment, I strain relieved the wires and verified
that all the components would survive high RPM vibrations. I even glued some
in place, including the two socket mounted IC's. Some R/C Rx foam padding
was used to protect the boards in the Pactec Box.
Both Boards Sandwiched
Mounted in the Pactec
Finished unit shown
The technical details
are available as file downloads. There is no charge for the information when
used in a personal (hobby) project. Commercial users must obtain written
approval before use.
Please be aware that
the information is copyright protected, so you are not authorized to republish
it, distribute it, or sell it, in any form. If you wish to share it, please
do so only by providing a link to the RC-CAM site. You are granted permission
to post links to the web site's main page
Please respect this simple request.
Files: PDF file of the HamCam-ID'er circuitry. All components are from
Revision: Rev A, dated 03-18-2002
Code: Hex file of the compiled HamCam-ID'er firmware. You should occasionally
check for updates.
The Small Print:
|If you need a part
then please consult the sources shown in the project (see schematics download).
I do not work for, nor represent, ANY supplier of the parts used in HamCam-ID'er.
Any reference to a vendor is for your convenience and I do not endorse or
profit from any purchase that you make. You are free to use any parts source
that you wish.
All information is
provided as-is. I do not offer any warranty on its suitability. That means
that if you build and use this device, you will do so at your own risk. If
you find software bugs then please report them to me.