OPTIONAL: COMMUNICATION WITH COMPUTERS WHEN THESE ARE AVAILABLE AND FUNCTIONING PROPERLY.
OPTICAL COUPLER FOR TRANSFERRING DATA BETWEEN MEDICATION MONITORS AND COMPUTERS.
Introduction: Basic means to view the adherence record without computers or PDAs
Many, if not most, clinics and community workers in developing countries do not have computers or PDAs. When these devices are available they are often broken, lost, or stolen. Therefore, this website has described how a red/green/yellow LED could be built into a medication monitor and used to view the patient's adherence record without these external devices. This is the simplest and most practical means by which the adherence record can be viewed in most settings and will always be available even if computers and PDAs are being used and are lost, stolen, or broken.
Using an Optical Coupler to link the Monitor to a Computer
In more advanced operations when computers are readily available they could and probably should be used. To accomplish this the red light emitted by the red/green LED could be used to transmit data as a series of pulses to an optical coupler that would further transmit the data to the computer.
To make the optical coupler maximally useful if should probably be a stand-alone portable device with internal memory. For technical reasons discussed in Design Considerations, it would be best if the coupler were designed to talk both ways between the medication monitor and the computer. Such a coupler could
1) Collect data from the medication monitor and transfer it to a computer.
2) Transmit data and instructions to a medication monitor,
Examples of collecting data from the monitor.
1) The community worker could use the portable optical coupler to collect the adherence record from all of his or her patients and transfer the record to the computer in the clinic when he or she visits the clinic. The coupler would also collect and transfer the identification number of the monitor, the time when the community worker collected data, proving the community worker visited the patient that day. Note: the computer would keep the identification number of the medication monitor that was given to the patient so the data for each patient could be compiled and displayed in one place.
2) If the patient brought the medication monitor into the clinic, an optical coupler kept in the clinic could be used to transfer data from the monitor to the computer. To prevent its loss, this optical coupler should probably be lashed to the computer.
3) The optical coupler could also collect and transfer other types of data such as the HIV and sputa status. The reason for keeping such data in the monitor is to have it available in case the clinic records were lost or the patient moved to a new clinic.
Examples transmitting data and instructions to the monitor.
1) The optical coupler could transmit data, such as the HIV and sputa status, to the monitor.
2) The optical coupler could transmit directives to the monitor for the time to activate the LED and buzzer, signals that can be used to instruct and remind the patient when to take medication.
3) The optical coupler could transmit an indication of the quantity and time that the monitor had been filled. The monitor would keep the time and date it was filled. This data could enable the monitor to remind the patient to return to the clinic for refills of medication by flashing the LED yellow starting a few days before he is scheduled to return.
4) If the coupler had an identification number, the introduction of the coupler would create an indication that a specific caregiver had queried the monitor and the monitor would record the time when this happened.
5) In situations where it is critical that DOT be given without fail like the treatment of multi drug resistant TB, the optical coupler that is kept by a community worker could be adapted to unlock a mechanism that permits removal of medication. One such mechanism permits the advancement of the cover of the UBox developed by a group at MIT that would prevent the patient from removing and discarding the medication before the caregiver arrived and represent further proof that the caregiver was present to give the DOT. http://www.innovatorsinhealth.org/, In case the caregiver was unable to visit the patient, the monitor could be programmed to unlock itself in the evening so the patient could still get the prescribed medication.
To accomplish these "instruction features" the optical coupler could have multiple input buttons or one input button with multiple functions which would be introduced by having the caregiver introduce different codes.
As work proceeds additional applications of the optical coupler will most likely appear.
While the portable optical coupler could be lost, it is unlikely that it would be stolen, because except for the battery, it would have no market value. If the optical coupler was lost, the community or clinic worker could still obtain the adherence record by viewing the red/green LED.
It is estimated that an optical coupler could be manufactured for $10.00 to $15.00 in mass production
Finally, it needs to be stressed that the red/green/yellow LED can accomplish the essential function of presenting the adherence record and many of the functions listed above without using an optical coupler and a computer.
DESIGN CONSIDERATIONS
The following material presents some general design considerations for an optical coupler but does not get into all the details of the actual design.
1. THE PHOTOSENSOR (THE FRONT END)
Silicon photodiodes and phototransistors are sensitive to visible light and near infrared. Typically they are most sensitive in the near infrared somewhere in the 800 - 900 nanometer range and have decreasing sensitivity on each side of this maximum. With both red and green LEDs available in the monitor, using the red LED for data transmission will be the clear choice since the sensor will be more sensitive to red light than to green. A sensor with its peak sensitivity at 800 nm looking at the red LED would have 40 to 60% percent of its maximum sensitivity. Silicon photodiodes and phototransistors also have relatively fast response times making them suitable as sensors for receiving data.
The sensor circuit is very simple. Connecting a photodiode or phototransistor in series with a resistor creates a voltage divider. The output of the circuit is the voltage at the point between the two, referenced to the power source "common". If the photodiode or phototransistor is connected to the positive supply (typically 3 or 5 volts) and the resistor is connected to the power source common, the circuit would function as follows: When the photodiode or phototransistor is illuminated, it permits a relatively large current to flow and in effect acts as a small resistor. With this small resistor connected to the positive supply and a much larger resistor connected to common, the output voltage is close to the positive supply voltage (indicating logic one). When the photodiode or phototransistor is in the dark, it permits only a very small current to flow and acts as a large resistor. With this large resistor connected to the positive supply and a much smaller resistor connected to common, the output voltage is close to zero (logic zero).
Typically, the resistor would cost around 5 cents and the phototransistor can be under $1. A possibly suitable phototransistor would be Panasonic PNZ147 which would cost $0.78 each in 10,000's. (For specifications, see: http://rocky.digikey.com/weblib/Panasonic/Web%20data/PNZ147.pdf)
Since a phototransistor such as the PNZ147 would be sensitive to ambient light, the optical coupler would incorporate a means of excluding ambient light when it is connected to the monitor. This could be simply a soft cup which mates with the monitor surface.
2. THE SIMPLEST BUT IMPRACTICAL COMPUTER INTERFACE
With the circuit described above, the simplest computer interface would be achieved by connecting the circuit's output to an input line to the computer's processor. The processor would then sample this input periodically to receive the transmitted data.
A couple problems make this simplest interface impractical:
First, the processor must know when to sample the input in order to receive valid data.
When the monitor is instructed to transmit data by someone in the clinic entering a code through the switch button, the monitor might transmit its data by first sending a unique pattern of light pulses indicating that it was beginning to transmit data. In preparation for recognizing this pattern, the processor would already need to be sampling its input to detect the pattern. Once this pattern was transmitted, the monitor might turn the red LED on or off at regular intervals (say, every 0.1220703 milliseconds) to transmit successive bits of data. The processor would need to use the initial pattern to know when to start receiving data, and would then need to have a time reference accurately matching the transmission times. But, the processors in many computers may not have an available time reference for matching the times of data transmission (e.g. 8.192 kHz for sampling every 0.1220703 milliseconds).
Second, processor input lines are not easily accessible in most computers manufactured within the past 20 years; and those inputs are usually dedicated to other functions.
3. HANDSHAKING (FLOW CONTROL)
The problem of synchronizing reading of the transmitted data with the times when data is transmitted was described in the previous section. This problem could be overcome to a large extent if the device receiving the data (the processor in the above discussion) was able to "talk to" the monitor. Then, the receiver could transmit a signal to the monitor indicating that it was ready to receive data, and the monitor could respond by sending a packet of data (handshaking, or flow control). This requires that the monitor be able to accept a digital input from the device receiving the monitor's data.
It would be convenient to use optical coupling to transmit signals to the monitor. The best choice for this would be in infrared LED in the receiving device and an infrared photodiode or phototransistor in the monitor. (Infrared phototransistors incorporate an optical filter which transmits a narrow band of wavelengths matching the wavelength of the infrared LED, often 880 nm. This greatly reduces effects from ambient light.)
Since infrared phototransistors and LEDs are widely used, they are quite inexpensive. One inexpensive infrared LED is the Fairchild QEC113. (For specifications, see: http://www.fairchildsemi.com/ds/QS/QSC112.pdf.) In 10,000 quantities, these cost also only 7.13 cents each. The matching phototransistor which should be suitable for use in the monitor would be a the Fairchild QSC113 (For specifications, see: http://www.fairchildsemi.com/ds/QS/QSC112.pdf) In 10,000 quantities, these also cost also only 7.13 cents each. Thus, adding optical data input to the monitor might add as little as 12.13 cents (7.13 + 5) to the cost of the monitor.
The ability of the monitor to receive data through an optical link offers several other advantages:
a) It could be relatively simple to transmit the patient's identifying information and clinical data to the monitor so that data could be stored in the monitor.
b) It could be easy to transmit data to the monitor indicating when the monitor was refilled; and that information could be stored in the monitor.
c) By knowing when data was retrieved from the monitor, the monitor could retain a record of when it had been queried.
d) If each caregiver had a stand-alone device which could communicate with the monitor, caregiver visits could be recorded by the monitor.
4. THE PREFERRED COMPUTER INTERFACE
Obviously, the optical coupler should connect to the host computer through a standard connection which is available on virtually all computers using a standard interface. For much of the time that computers have been available, the ubiquitous interface has been the RS-232 serial port. However, this is being supplanted by the Universal Serial Bus (USB) which is available on most computers manufactured within the past 10 years. Looking forward, RS-232 is likely to become available on fewer and fewer computers, while USB remains ubiquitous. So, it would make very good sense for the optical coupler to incorporate a USB interface.
One "low cost" USB controller is the Maxim MAX3420E (For specifications, see: http://pdfserv.maxim-ic.com/en/ds/MAX3420E.pdf.) This USB controller connects to a microcontroller and manages communication between the microcontroller and the computer's USB port. In the case of the optical coupler, the microcontroller would serve as the interface between the optical link(s) and the USB controller. With these components, a simplified diagram of the optical coupler would look like this:
[Optical Sensor(s)] <---> [Interface Microcontroller] <---> [USB Controller]
In quantities of 100, the MAX3420E would cost $3.51 each.
The interface microcontroller will need to be selected to meet the system requirements. There are around 20,000 different microcontrollers available, ranging in cost from under $1 to over $30. Some incorporate their own USB controller which could reduce the parts count, though not necessarily the cost.
At this point, I would offer a wild guess that the parts for the optical coupler will cost in the neighborhood of $10 in production quantities.
5. THE OPTICAL COUPLER AS A STAND-ALONE DEVICE ?
Quite frequently, USB devices which connect to a computer are powered by the host computer with power supplied through the USB connector. If the optical coupler is always used with a computer, it would make good sense to do this. However, there may be advantages to powering the optical coupler with its own battery so that it can be used independently. As an example, a caregiver could use a stand-alone optical coupler with sufficient memory to collect compliance data from all of the patients she visits. This could later be uploaded to a computer in the clinic to provide the clinic with more data more frequently than the patient's clinic visits.
While the discussion above mentions some specific components, these have been included only for the purpose of indicating representative component prices. This discussion of design considerations does not provide the details of an actual design. The final selection of components and the design of the circuit into which they would be incorporated would require a careful engineering design effort which would take into account a variety of technical factors, as well as cost.
Finally, it has been suggested that all or most of the functions of the optical coupler could be achieved by having an RFD reader in the computer and incorporated in the care giver's portable device with an RFD tag in the medication monitor. The individual who made this suggestion is Mr. Michael Peterson at Information Medially in Ottawa Canada. His E-mail address is Mpetersen@informationmediary.com
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DISPLAYS INCORPORATED INTO COMPLIANCE MONITORS