Journal of Medical Engineering & Technology
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
A low cost portable enuresis alarm G. Manson & J. Read To cite this article: G. Manson & J. Read (1979) A low cost portable enuresis alarm, Journal of Medical Engineering & Technology, 3:2, 83-84, DOI: 10.3109/03091907909161618 To link to this article: http://dx.doi.org/10.3109/03091907909161618
Published online: 09 Jul 2009.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [Flinders University of South Australia]
Date: 25 March 2016, At: 22:02
A low cost portable enuresis alarm G.Manson, MSc, BEng, CEng, MIEE and J. Read. Area Medical Physics Service, Musgrove Park Hospital, Taunton, Somerset, TAl SDA
Downloaded by [Flinders University of South Australia] at 22:02 25 March 2016
The enuresis alarm described is a portable device designed for ‘toilet training’ of mentally sub-normal children. It weighs 70gm with battery, has dimensions of 90 x 60 x 30 mm and conforms to DHSS recommendations. The battery life is over 1000 hours (6 weeks) in continuous use. Total component cost is 26.20 (in 1978), construction is simple and the circuit may be used as a conventional nocturnal enuresis alarm.
activated, the alarm should latch on and light a pilot light as well as make a noise. The pad resistance range is specified for reliability, as too sensitive alarms (high resistance) are liable to give false alarms in damp atmospheres o r because of perspiration, and insensitive alarms (low resistance) will not detect slight micturition, although latching improves reliability in such cases. No commercial alarm is small enough for ambulent use so the unit described here was designed for use by sub-normal children during bladder-training. The alarm may also be useful for normal children requiring a nocturnal alarm when conventional pads and wet bed linen are not acceptable (for example during holidays). The circuit is ideal for small scale production and may be used to build a conventional alarm unit (using a 6 V lantern battery, instead of the 4 V battery used in this circuit and a pilot bulb).
The pads
Introduction Enuretic alarm trainers have been produced for many years as nocturnal bladder training aids [ 11. These are available commercially at low cost and work by detecting urine when it contacts two metal gauze pads, separated by a normally dry sheet. Most commercial alarms work by detecting the change in voltage across the pads as the resistance drops (a small current being fed through the pads). One alarm, however, uses dissimilar metal gauze pads and detects the voltage created by electrolytic action. The crudest alarm operates a relay directly via the pads; the relay latching when activated and turning on a lamp and bell or buzzer. Such alarms should not be used as the high pad current (2 to 3 mA) can cause ‘buzzer ulcers’ on the subject who makes contact with the pad. The DHSS has produced a specification for enuretic alarms [ 21 which require the current in the pad t o be below lOOpA and also recommends that the alarm should work when the When inter pad resistance is between 1 0 k a and 250
a.
The pad is made from t w o strips of terylene fabric coated with conducting rubber. The strips (90 mm x 5 mm) have a resistance of S O O n and have insulated wire stapled to them. They are stuck 2mm apart on standard 1 inch ‘Sleek’ tape, the staples are coated with Silcoset 151 (ICI) and the whole pad is covered with absorbant soft paper. They may be used inside standard underwear o r in incontinence pants (such as Kanga Marsupial). The pads are disposed of after use, each pad only taking two minutes to make at a material cost of 2 pence.
Circuit description The circuit, shown in Figure 1, uses two resistor networks, one quad amplifier IC, two capacitors, one diode and an E-line transistor. The L M 3302 amplifier, a quad open collector amplifier, uses only 0.8 mA and is designed to operate with a supply of between 2 and 28 volts.
Figure I . Circuit diagram of alarm
I
Besson
vs
I
vs
BCX38C
y; 3
Quad amplifier LY3302
Reststor networks
Beckrnan 898-3 - R 1 0 0 K
1
Volume 3 No. 2 March 1979
83
Downloaded by [Flinders University of South Australia] at 22:02 25 March 2016
Manson and Read - Portable eneuresis alarm
Amplifiers 2 and 3 are square wave oscillators with frequencies of 2 Hz and 2 kHz respectively. The triangular wave form signals taken from the inverting inputs are compared by amplifier 4 and produce a 2 kHz output signal, width modulated at 2 Hz. When this signal operates the sound transducer, via a buffer Darlington transistor, a penetrating sound results. The output transistor is, however, held off by input amplifier 1 until the pad resistance is lowered. When the alarm is first switched on, with high resistance (dry) pads, the output of amplifier 1 remains at near zero volts, as the load capacitance and slew rate limit results in the non-inverting input voltage rising at a slower rate than the inverting input. The switching threshold of amplifier 1 is determined by the voltage on the non-inverting input (which is the ‘output saturation voltage plus oscillator noise pick up) and the offset voltage. The spread of amplifier characteristics results in a threshold of between 9 mV and 45 mV, with a pad current of 40 pA (via the iOOkS?resistor from the 4 volt power supply) and this threshold is reached with a pad resistance between 250Q and 1.1 kQ. The resistance required is not greatly affected by the supply, as pad voltage, noise and saturation voltage are all proportional to the battery voltage. When the output of amplifier 1 goes high, it latches by taking the non-inverting input up to the supply voltage. For use in damp houses, or with a perspiring subject, an insensitive circuit is useful. But for use with the conducting rubber pads where greater sensitivity is required, a 2 p F capacitor is inserted as shown in the circuit diagram (this can be etched on the printed circuit board). This feeds pulses of about 200 mV to the non-inverting input (which has an input capacitance of about 4 0 pF). Thus a pad resistance of about 6kfl causes the alarm to operate.This sensitivity is necessary for use with the rubber pads and is also best suited for conventional pads when the circuit is used in a bedside alarm and will allow even very slight leakage to be detected. The low sensitivity circuit, without the feedback capacitor, is not as good at detecting slight leakage but allows an alarm to be successfully employed in damp houses or with perspiring subjects. The circuit with the feedback capacitor has a stable operating point independent of supply voltage (pad voltage and oscillator pulses are both proportional to supply voltage)
I
Lorespondence Some experience in fitting a myoelectrically controlled hand which has a sense of touch Dear Sir, Dr. Shannon’s recent paper [ 11 was of considerable interest here because of the great similarity between our respective efforts to develop clinically-valuable sensory feedback for myoelectric prostheses. However, one section of that paper, concerning our problem with a 1974 system, is quite misleading and deserves explanation. The facts are as follows. In January 1973 a fourteenyear-old girl with a congenital left below-elbow amputation was fitted with a myoelectrically controlled prosthesis. This incorporated a UNB 3-state control unit which used
84
and, as the input capacitance spread is not large, operation with a pad resistance between 3.5 kQ and 7 k f l occurs with any amplifier. The pad current is proportional to the supply voltage and would be 100 p A with a 10 volt supply, so when used with a 6 volt supply and a pilot lamp across the sound transducer, for a conventional alarm, the circuit meets all the recommendations for a nocturnal enuresis alarm and will operate even at an end of battery life voltage of 3 V. The alarm circuit, although apparently complex, requires only seven components to be mounted on the circuit board and is, therefore, ideal for small scale production. The portable alarms, using pre-drilled boxes and printed circuit boards, were assembled in about 1 5 minutes at a component cost of €6.20.
Discussion The four alarms made for the clinical trial (all of which triggered the alarm at about 6.8 k a ) performed well, fitting easily in a pocket and producing an easily heard noise. A battery life of nearly 18 weeks can be achieved with a TRl13N battery used 8 hours per day, so attention by skilled staff is needed very infrequently. The original portable units were used under supervision so were not made watertight but, for use in the home, waterproofing is advisable. Such a unit for nocturnal use with pilot lamp and PJ996 lantern battery could be constructed at a component cost of about E8 and would be a high quality unit with a battery life of about one year.
ACKNOWLEDGEMENTS Mr. D. Southwart of Dunlop Ltd. (Precision Rubber Division, Shepshed, Loughborough) kindly supplied conducting rubber sheet.
REFERENCES [ I ] Glen E.S. and Rowan D, (1974) Enuretic Alarm Trainer for night and day, Lancet, Oct. 26, pp 987-988. [ 21 Enuresis Alarms: A Performance Specification. (1968) DHSS R/E1004103 February.
recessed Silver Silver-Chloride electrodes and a conductive gel (EKG Sol, by Burton Parsons). This fitting was successful and the prosthesis was worn regularly. In June 1974 the prosthesis was replaced with an experimental unit incorporating an electrocutaneous feedback system, using the same electrodes both for feedback and control (on a time-shared basis). No change was made either in electrode type, location, or conductive gel. The fitting was successful, the patient being very happy with the addition of feedback despite some initial adjustment problems, [ 21. In September 1974 this patient developed a severe rash covering her stump. It was determined that she had developed a contact dermatitis, apparently due to an allergic reaction to the electrodes and/or the conductive gel. Perhaps because of the severity of the reaction, substituting other electrodes and/or other electrode gels did not relieve the problem. For some time she went without a prosthesis. In June 1975, with her stump well healed, she was fitted with a passive cosmetic prosthesis with a silicone rubber socket. This was tolerated without problem, and in February 1976 it was replaced with a new prosthesis using a revised UNB 3-state control system with “dry” electrodes. Normally stainless steel electrodFs were used with this system. However, in view of this patient’s history, gold-plated electrodes were used. The fitting was successful. Journal of Medical Engineering and Technology
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
A low cost portable enuresis alarm G. Manson & J. Read To cite this article: G. Manson & J. Read (1979) A low cost portable enuresis alarm, Journal of Medical Engineering & Technology, 3:2, 83-84, DOI: 10.3109/03091907909161618 To link to this article: http://dx.doi.org/10.3109/03091907909161618
Published online: 09 Jul 2009.
Submit your article to this journal
Article views: 1
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [Flinders University of South Australia]
Date: 25 March 2016, At: 22:02
A low cost portable enuresis alarm G.Manson, MSc, BEng, CEng, MIEE and J. Read. Area Medical Physics Service, Musgrove Park Hospital, Taunton, Somerset, TAl SDA
Downloaded by [Flinders University of South Australia] at 22:02 25 March 2016
The enuresis alarm described is a portable device designed for ‘toilet training’ of mentally sub-normal children. It weighs 70gm with battery, has dimensions of 90 x 60 x 30 mm and conforms to DHSS recommendations. The battery life is over 1000 hours (6 weeks) in continuous use. Total component cost is 26.20 (in 1978), construction is simple and the circuit may be used as a conventional nocturnal enuresis alarm.
activated, the alarm should latch on and light a pilot light as well as make a noise. The pad resistance range is specified for reliability, as too sensitive alarms (high resistance) are liable to give false alarms in damp atmospheres o r because of perspiration, and insensitive alarms (low resistance) will not detect slight micturition, although latching improves reliability in such cases. No commercial alarm is small enough for ambulent use so the unit described here was designed for use by sub-normal children during bladder-training. The alarm may also be useful for normal children requiring a nocturnal alarm when conventional pads and wet bed linen are not acceptable (for example during holidays). The circuit is ideal for small scale production and may be used to build a conventional alarm unit (using a 6 V lantern battery, instead of the 4 V battery used in this circuit and a pilot bulb).
The pads
Introduction Enuretic alarm trainers have been produced for many years as nocturnal bladder training aids [ 11. These are available commercially at low cost and work by detecting urine when it contacts two metal gauze pads, separated by a normally dry sheet. Most commercial alarms work by detecting the change in voltage across the pads as the resistance drops (a small current being fed through the pads). One alarm, however, uses dissimilar metal gauze pads and detects the voltage created by electrolytic action. The crudest alarm operates a relay directly via the pads; the relay latching when activated and turning on a lamp and bell or buzzer. Such alarms should not be used as the high pad current (2 to 3 mA) can cause ‘buzzer ulcers’ on the subject who makes contact with the pad. The DHSS has produced a specification for enuretic alarms [ 21 which require the current in the pad t o be below lOOpA and also recommends that the alarm should work when the When inter pad resistance is between 1 0 k a and 250
a.
The pad is made from t w o strips of terylene fabric coated with conducting rubber. The strips (90 mm x 5 mm) have a resistance of S O O n and have insulated wire stapled to them. They are stuck 2mm apart on standard 1 inch ‘Sleek’ tape, the staples are coated with Silcoset 151 (ICI) and the whole pad is covered with absorbant soft paper. They may be used inside standard underwear o r in incontinence pants (such as Kanga Marsupial). The pads are disposed of after use, each pad only taking two minutes to make at a material cost of 2 pence.
Circuit description The circuit, shown in Figure 1, uses two resistor networks, one quad amplifier IC, two capacitors, one diode and an E-line transistor. The L M 3302 amplifier, a quad open collector amplifier, uses only 0.8 mA and is designed to operate with a supply of between 2 and 28 volts.
Figure I . Circuit diagram of alarm
I
Besson
vs
I
vs
BCX38C
y; 3
Quad amplifier LY3302
Reststor networks
Beckrnan 898-3 - R 1 0 0 K
1
Volume 3 No. 2 March 1979
83
Downloaded by [Flinders University of South Australia] at 22:02 25 March 2016
Manson and Read - Portable eneuresis alarm
Amplifiers 2 and 3 are square wave oscillators with frequencies of 2 Hz and 2 kHz respectively. The triangular wave form signals taken from the inverting inputs are compared by amplifier 4 and produce a 2 kHz output signal, width modulated at 2 Hz. When this signal operates the sound transducer, via a buffer Darlington transistor, a penetrating sound results. The output transistor is, however, held off by input amplifier 1 until the pad resistance is lowered. When the alarm is first switched on, with high resistance (dry) pads, the output of amplifier 1 remains at near zero volts, as the load capacitance and slew rate limit results in the non-inverting input voltage rising at a slower rate than the inverting input. The switching threshold of amplifier 1 is determined by the voltage on the non-inverting input (which is the ‘output saturation voltage plus oscillator noise pick up) and the offset voltage. The spread of amplifier characteristics results in a threshold of between 9 mV and 45 mV, with a pad current of 40 pA (via the iOOkS?resistor from the 4 volt power supply) and this threshold is reached with a pad resistance between 250Q and 1.1 kQ. The resistance required is not greatly affected by the supply, as pad voltage, noise and saturation voltage are all proportional to the battery voltage. When the output of amplifier 1 goes high, it latches by taking the non-inverting input up to the supply voltage. For use in damp houses, or with a perspiring subject, an insensitive circuit is useful. But for use with the conducting rubber pads where greater sensitivity is required, a 2 p F capacitor is inserted as shown in the circuit diagram (this can be etched on the printed circuit board). This feeds pulses of about 200 mV to the non-inverting input (which has an input capacitance of about 4 0 pF). Thus a pad resistance of about 6kfl causes the alarm to operate.This sensitivity is necessary for use with the rubber pads and is also best suited for conventional pads when the circuit is used in a bedside alarm and will allow even very slight leakage to be detected. The low sensitivity circuit, without the feedback capacitor, is not as good at detecting slight leakage but allows an alarm to be successfully employed in damp houses or with perspiring subjects. The circuit with the feedback capacitor has a stable operating point independent of supply voltage (pad voltage and oscillator pulses are both proportional to supply voltage)
I
Lorespondence Some experience in fitting a myoelectrically controlled hand which has a sense of touch Dear Sir, Dr. Shannon’s recent paper [ 11 was of considerable interest here because of the great similarity between our respective efforts to develop clinically-valuable sensory feedback for myoelectric prostheses. However, one section of that paper, concerning our problem with a 1974 system, is quite misleading and deserves explanation. The facts are as follows. In January 1973 a fourteenyear-old girl with a congenital left below-elbow amputation was fitted with a myoelectrically controlled prosthesis. This incorporated a UNB 3-state control unit which used
84
and, as the input capacitance spread is not large, operation with a pad resistance between 3.5 kQ and 7 k f l occurs with any amplifier. The pad current is proportional to the supply voltage and would be 100 p A with a 10 volt supply, so when used with a 6 volt supply and a pilot lamp across the sound transducer, for a conventional alarm, the circuit meets all the recommendations for a nocturnal enuresis alarm and will operate even at an end of battery life voltage of 3 V. The alarm circuit, although apparently complex, requires only seven components to be mounted on the circuit board and is, therefore, ideal for small scale production. The portable alarms, using pre-drilled boxes and printed circuit boards, were assembled in about 1 5 minutes at a component cost of €6.20.
Discussion The four alarms made for the clinical trial (all of which triggered the alarm at about 6.8 k a ) performed well, fitting easily in a pocket and producing an easily heard noise. A battery life of nearly 18 weeks can be achieved with a TRl13N battery used 8 hours per day, so attention by skilled staff is needed very infrequently. The original portable units were used under supervision so were not made watertight but, for use in the home, waterproofing is advisable. Such a unit for nocturnal use with pilot lamp and PJ996 lantern battery could be constructed at a component cost of about E8 and would be a high quality unit with a battery life of about one year.
ACKNOWLEDGEMENTS Mr. D. Southwart of Dunlop Ltd. (Precision Rubber Division, Shepshed, Loughborough) kindly supplied conducting rubber sheet.
REFERENCES [ I ] Glen E.S. and Rowan D, (1974) Enuretic Alarm Trainer for night and day, Lancet, Oct. 26, pp 987-988. [ 21 Enuresis Alarms: A Performance Specification. (1968) DHSS R/E1004103 February.
recessed Silver Silver-Chloride electrodes and a conductive gel (EKG Sol, by Burton Parsons). This fitting was successful and the prosthesis was worn regularly. In June 1974 the prosthesis was replaced with an experimental unit incorporating an electrocutaneous feedback system, using the same electrodes both for feedback and control (on a time-shared basis). No change was made either in electrode type, location, or conductive gel. The fitting was successful, the patient being very happy with the addition of feedback despite some initial adjustment problems, [ 21. In September 1974 this patient developed a severe rash covering her stump. It was determined that she had developed a contact dermatitis, apparently due to an allergic reaction to the electrodes and/or the conductive gel. Perhaps because of the severity of the reaction, substituting other electrodes and/or other electrode gels did not relieve the problem. For some time she went without a prosthesis. In June 1975, with her stump well healed, she was fitted with a passive cosmetic prosthesis with a silicone rubber socket. This was tolerated without problem, and in February 1976 it was replaced with a new prosthesis using a revised UNB 3-state control system with “dry” electrodes. Normally stainless steel electrodFs were used with this system. However, in view of this patient’s history, gold-plated electrodes were used. The fitting was successful. Journal of Medical Engineering and Technology
