 Aaron’s Clock, No-Hands Required
This project was submitted to Parallax by Mark Spencer, WA8SME
Typical of any new Ham, Aaron, KD7UCD, wants to operate his station in accordance with the FCC regulations and in a responsible manner. He also is enthusiastic about participating in all of the public service operation opportunities that are open to him now that he is a Ham including ARES and SKYWARN. Unlike the typical Ham though, Aaron is blind, which complicates many things for him. Aaron, and others like him, inspired the no-hands clock. Micro-controller technology is very powerful, flexible, adaptable, and relatively inexpensive. This microcontroller based project allows Aaron to determine the current time, outside temperature, and when it is time to ID his station at the touch of a button. The information is announced by audio tone Morse code, hence no-hands are required. Because there are mobility issues, this project also uses wireless technology to allow the user to query the no-hands clock through a pocket sized, key fob transmitter.
Circuit Description
 The circuit diagram in figure 1 also serves as a block diagram of the no-hands clock for the following overview discussion. The central component of the no-hands clock is a BASIC Stamp® 2 module. The BS2 communicates with and controls the other components of the no-hands clock by serial communication. In turn, the BS2 communicates with the user through Morse code. The Dallas Semiconductor DS1302 device is a Trickle Charge Timekeeping Chip that provides a real time clock. The Dallas DS1620 Digital Thermometer and Thermostat Chip is remoted from the no-hands clock to provide outside air temperature data. The Parallax RF Keychain receiver (#28004) and transmitter (#28005) pair provide the remote control interface for the circuit. Of course the real brains behind this simple circuit is in the software. I will not detail the software in this article because the program listing has extensive documentation. The builder should be able to review the software comments and gain an understanding of the logic and commands used to make the no-hands clock work. A 9-volt DC, wall plug, power cube, powers the clock. The current requirement is approximately 15mA. This wall-power source is backed up by a 9-volt battery that is isolated by a diode until a main power failure occurs. The internal voltage regulator of the BS2 reduces and regulates the 9-volt wall-power source to 5-volts, which in turn becomes the power source of the other no-hands clock components. The BS2 communicates with the user via the speaker or buzzer. Audible “beeps” indicate when switches are pressed or Morse code is sent to report the requested data. The BS2 communicates with the DS1302 and DS1620 devices through a simple serial bus. Common clock and data lines are shared between the devices with unique chip-select lines used to address the discrete device.
The DS1302 clock chip requires only an external crystal to drive an internal oscillator to operate. The resistor tied to the I/O pin provides current limiting protection in case the BS2 data line somehow gets out of sync with the DS1302. When power is first applied, the clock time is set to all zeros. The series of four momentary-ON SPST switches connected to the BS2 are used to set the clock time. Each switch is pressed to advance the appropriate time digit one digit at a time (i.e., 10’s hr, 1’s hr, 10’s min, 1’s min). The clock is programmed through software for a 24-hour format. When the user requests a reading of the time, a command is sent by the BS2 to the chip and then receives the current time from the chip. Only the hour and minute digits are used in this project, the other digits of day, date, and seconds are disregarded. The time is sent by the chip in BCD and ASCII format so that the digits are ready for visual display. The BS2 program converts this format into numbers 0 through 9 that are in turn transmitted in Morse code.
 The DS1620 thermometer chip requires only the current limiting resistor on the I/O line and a power supply bypass capacitor mounted at the device between Vcc and ground for operation. The chip is mounted in a weather resistant housing and connected to the BS2 by a length of multi-conductor wire so that the chip can be mounted outside of the shack. I used a ‘AA’ cell battery holder for the housing that is painted white to deal with radiation absorption complications that would prevent accurate temperature measurements. The chip requires initial programming when it is first put into service. The chip has numerous modes of operation; in the no-hands clock application, the free-running mode is used. When the user requests a reading of the temperature, a command is sent by the BS2 to the chip and it receives the current temperature from the chip in two’s compliment binary data of the temperature in degrees Centigrade. The BS2 program accomplishes binary arithmetic to convert the temperature into Fahrenheit and both temperature readings (F and C) are transmitted by Morse code.
The user accesses the no-hands clock through a wireless connection made up of a small receiver that is connected to the BS2 and a hand held transmitter that resembles the car door locking, key fob transmitter common to most car remote control locking systems. The user pushes the appropriate button on the transmitter, and the corresponding line on the receiver goes to high state (+5 volts). The BS2 constantly polls the receiver lines looking for a command to execute in response to the user’s input. The range of the transmitter is advertised to be 75 feet. However, being within earshot of the no-hands clock is far enough for this application.
 No-Hands Clock Construction and Start-up
Refer to the accompanying photos of the project to see how the no-hands clock is constructed and housed in its final form. The wiring of the circuit is not critical. I used wire wrap connections between points. The BS2 should be socketed so that it can be easily removed for programming. A buzzer is used for the speaker source in this project to limit current requirements; the tradeoff is that the buzzer fixes the frequency. Other buzzer frequencies are available as desired by the builder. If additional frequency agility is needed, a piezo speaker can be substituted. A few lines of code will need to be changed if this substitution is made as documented with the software.
When the BS2 is first programmed, be sure to include the indicated four lines of code that are commented out in the final version of the software. These four lines of code accomplish two things that need to be done only one time. First, a memory location is used in the BS2 to store and hold the previous code transmission speed. Two lines of code put an initial number value in the memory location, subsequent user changes in the code speed will change this value and therefore those two lines of code will not be required. Two lines of code are needed to place a ‘fresh’ DS1620 chip in the continuous mode of operation. This mode is maintained in the chip’s internal non-volatile RAM, even if power is lost, therefore the two lines of code will not be required after the DS1602 is initialized. After the BS2 is first programmed and run, the four lines can be commented out and the BS2 reprogrammed for the final time.
Operation
Operation of the no-hands clock is straightforward. Once power is first applied or after a total power failure, the DS1302 clock chip will need to be set to the current time. The four momentary-ON switches are pressed to advance the appropriate time digit (in a 24-hour clock format). The BS2 provides audio feed back with a ‘beep’ each time a button is press. The backup battery should maintain the clock time during a main power failure.
To access the time, press key button 1 on the transmitter. The time will be sent via Morse code. Pressing key button 2 will activate a 10 minute timer. When activated, the BS2 transmits a single ‘beep.’ Each passage of the 10 minute interval will be signaled by three beeps sent as the letter ‘S’ by the BS2. Pressing key button 2 again will turn off the ID timer and a double ‘beep’ will be sent by the BS2. While the no-hands clock is in the ID mode, the user can request the current time and temperature. Pressing key button 3 will request the temperature. The BS2 responds by sending the temperature in Fahrenheit first and then the temperature in Centigrade (i.e., 68 F / 20 C). If the temperature is negative, a leading ‘M’ will be added to the temperature digits. Pressing key button 4 changes the Morse code transmission speed in ten steps. When button 4 is pressed, the BS2 responds with the appropriate digit representing the code speed step 0 (the highest speed) through 9 (the slowest speed), sent at the step code speed. Keep pressing button 4 until the desired speed is reached. The no-hands clock defaults to the fastest speed because operator proficiency will improve with use. If higher speeds are desired, simply decrease the code speed number documented in the software listing and reprogram the BS2.
Because there was an extra key button and excess memory available in the BS2, one additional function was added. When button 5 is pressed, a unique personalized message is transmitted. The length of this message is limited by the amount of available memory. In this case, “KD7UCD DE WA8SME K” is the message sent (additional memory is available for a more lengthy message). The message can be easily changed when the BS2 is programmed. Software comments should help the user in making this change.
Teachers and Science Fair Participants.
Some of the concepts demonstrated in this project that provide an exceptional learning experience include:
- Adapting technology for disabilities
- Cultural diversity
- Computer programming
- Serial communications
- Computer bus communications
- Remote sensors
- Temperature conversions
- Two’s compliment mathematics
- BCD and ASCII code conversion
- Time formats
- Wireless technology
- Morse code
- Micro-controller technology
There are unlimited other possibilities. An exceptional adaptive circuit called Az ScQRPions Stinger Singer1, a CW audible frequency counter, could be interfaced with the no-hands clock to include an option to read (hear) the operating frequency. This kit project produces a frequency counter that samples the RF from the transmitter antenna feed line and reports the digits of the frequency to the user in Morse code. One channel of the key fob transmitter/receiver can be used to control this inexpensive addition to the visually impaired Ham shack. Other remote sensors can be added or substituted to adapt the circuit to the individual user.
The Value of Adaptive Technology
The no-hands clock project gave me a glimpse into the world of the visually impaired. Not only will this project help you learn about micro-controller technology but make you a better operator to boot. The no-hands clock is just a starting point that I hope will stimulate your imagination and perhaps encourage you to help others who need just a little different point of view to make Ham radio more enjoyable and more fulfilling.
The software to program the BS2 is available at the ARRL web site in file
No-hands clock.bs2. A Braille presentation of the clock operating instructions in Duxbury format that can be embossed for the visually impaired user is contained in file
clock instructions.dxb.
The ScQRPion Stinger Singer Frequency Counter is available through Bob Hightower, 1905 N. Pennington Dr., Chandler, AZ 85224, $20, postage and handling included.
A review of the Frequency Counter can be found at:
www.qrp-i.com/KA8MAV_SSS_Review.htm.
No-Hands Clock Unique Parts List
- Basic Stamp 2 Module, Digikey Corp., 701 Brooks Ave. S., POBox 677, Thief River Falls, MN 56701-0677, 1-800-344-4359, www.digikey.com.
- DS1302-ND, IC Timekeeper T-Charger 8-DIP, Digikey Corp.
- DS1620-ND, IC Thermometer/Stat DIG 8-DIP, Digikey Corp.
- 28004, 418 RX RF REC SIP/WIRE/SW, Parallax Inc., 599 Menlo Drive, Suite 100, Rocklin, CA 95765, 1-888-512-1024, www.parallax.com.
- 28005, 418 TX RF TM KC/LOOP/SW, Parallax Inc.
- Piezo Buzzer, 3-20 VDC, 2.7 kHz, 273-059, RadioShack.
- ‘AA’ Battery Holder, 270-409, RadioShack.
- DC Power Jack, Size K Coaxial, 274-1565, RadioShack.
- Interlocking Connectors, 274-236 and 274-226, RadioShack.
- 9V Battery Snap Connectors, 270-325, RadioShack.
A version of this article is also published in HOMEBREWER Magazine (www.amqrp.org/homebrewer/homebrewer.html) |