Med. & Biol. Eng. & Comput., 1979, 17, 277-278
Technical n o t e A simplified programmable calculator conversion for online measurement of miniature endplate-potential amplitudes K e y w o r d s - - M i n i a t u r e endplate-potential amplitudes, Programmable calculator conversion
THE measurement of miniature endplate-potential (m.e.p.p.) amplitude and frequency provides a valuable quantitative assessment of the integrity of the neuromuscular junction (FATT and KATZ, 1952; KATZ, 1966), but it is an extremely tedious task by hand methods. Such a measurement can be accomplished easily by a laboratory minicomputer. However, the cost for a minicomputer system can be in excess of $5 000. This report outlines the procedure for the low-cost (less than $700) conversion of a Hewlett-Packard 9800 series programmable calculator for the online measurement of m.e.p.p, amplitudes. Frequency counting can also be accomplished, provided that external timing is used. Once the m.e.p.p, amplitudes are stored within the calculator, the resident statistical routines can be employed. The m.e.p.p, amplitude-measuring system consists of peak-detecting and timing circuits (Fig. 1). A preampli-
~ t M ~ ~ + I 1OK
tier must be employed such that the amplified m.e.p.p. magnitudes fall within a range from 0-1 to 9"5 V. IC1, IC2, and IC3 form a simple peak-detecting and holding circuit. IC4, IC5, and IC7 form an eventmonitoring circuit which produces a start conversion pulse when the input signal exceeds a preset threshold level (see timing diagram in Fig. 1). The falling edge of the start conversion pulse (1 ms) initiates analogue-todigital conversion of the peak value. The falling edge of the end-of-conversion pulse (400 ns minimum) sets the flag line low, signalling the calculator to read the value on its input lines. The falling edge of the end-ofconversion pulse also triggers IC6 to produce a 1 ms reset pulse to discharge the peak holding capacitor, and the system is then ready to record the next m.e.p.p, amplitude. The highest rate at which the peak detector can function is 300 per second. However, the maximum data rate is set in this configuration by the data storage rate of the
1KSV 1M
2.2K HP
+
Ol,E
START CONVERSION
9810
ENDOF fLAG
IOK
....
-15V 15F ,
10K ~
lOOK
74121
2.5K I
O
§
I
9 ~10 K
K
START ~ CONVERSION
_
_
400nsec J~l __ 1 i RESET. . . . . . . . ~/msec[ ....
ENOOF CONVERSION lr 25X
1i
CONTROL
First received5th May and in final form 1lth July 1978
i
FLAGLOW
Fig. 1 Peak detecting and timing circuits for online measurement of m.e.e.p, amplitudes.
0140-0118/79/020277 -I- 02 $01 950/0
9 IFMBE: 1979 Medical & Biological Engineering & Computing
March 1979
277
calculator, and, for the 9810A, 40 per second is the maximum.Thus, any m,e.p.p, occurring within 25 ms of a previous one will not be counted. Transient signals which overflow are converted at the maximum level, but can be rejected by the analysis program. The circuit can be adjusted to measure the peak amplitude of any pulse with a rise time greater than 1 ms by modification of the timing circuit of IC7. Low-cost 741 operational amplifiers are used for IC1 to IC5. The 74121 1-shot multivibrator is used for IC6 and IC7. The analogue-todigital converter is a Datel ADC-89A eight-bit converter. The relay is a magnetic reed relay (Magnecraft W274 DPI-2), the diodes are 1N457s. The Hewlett-Packard 9810 programmable calculator employed in this application was also equipped with an eight-bit paralM-data-transfer interface card (HP 11202A) for data storage and analysis. An eight-bit analogue-todigital converter (Datel ADC-89A) was interfaced via the H P 11202A. The total cost of this system for measuring m.e.p.p, amplitudes was $634, including $500 for the interface card, $69 for the analogue-to-digital converter, $50 for the power supplies, and $15 for the circuit components. However, this circuit is not restricted to the H P 9810, for any calculator with an eight-bit parallel interface can be employed. The system as described is currently under continuous use and provides a significant cost and time savings over hand measurements from a strip-chart recorder and at far less cost than a conventional laboratory minicomputer system (SANDERSet al., 1976; KIM and SANDERS, 1978). Although this system was originally developed for the measurement of m.e.p.p, amplitude and frequency, it can be easily modified to measure other bioelectric events such as action potentials or endplate potentials. I n any situation where a HeMett-Packard 9800 series calculator is available, the small additional cost of
278
conversion is worthwhile. However, the Hewlett-Packard calculator does have speed and memory limitations and cannot be considered a complete replacement for a minicomputer.
Acknowledgment--This work was supported in part by a centre grant from the Muscular Dystrophy Association, Inc. and N I N C D S grant NS-12905.
g. CLINTONWILKINSON NIANCHANG EDITH COBB YONG I. KIM RICHARD N. JOHNSON
Department of Neurology and Division of Biomedical Engineering, University of Virginia Medical School, Charlottesville, Va. 22901, USA
References FATT,P. and KATZ,B. (1952) Spontaneous subthreshold activity at motor nerve endings. J. Physiok, 117, 109-128. KATZ, B. (1966) Nerve, muscle, and synapse. McGrawHill, New York. KIM, Y. I. and SANDERS, D. B. (1978) Experimental autoimmune myasthenia gravis: Effects of calcium and potassium on the spontaneous release ef neurom u ~ u l a r transmitter. Exp. Neurol., 61, 311-317. SANDERS, D. B., SCHLEIFER, L. S., ELDEFRAWI, M. E., NORCROSS,N. H., and COBB, E. E. (1976) An immunologically induced defect of neuromuscular transmission in rats and rabbits. Ann. N. Y. Acad. Sci., 274, 319-336.
Medical & Biological Engineering & Computing
March 1979
Technical n o t e A simplified programmable calculator conversion for online measurement of miniature endplate-potential amplitudes K e y w o r d s - - M i n i a t u r e endplate-potential amplitudes, Programmable calculator conversion
THE measurement of miniature endplate-potential (m.e.p.p.) amplitude and frequency provides a valuable quantitative assessment of the integrity of the neuromuscular junction (FATT and KATZ, 1952; KATZ, 1966), but it is an extremely tedious task by hand methods. Such a measurement can be accomplished easily by a laboratory minicomputer. However, the cost for a minicomputer system can be in excess of $5 000. This report outlines the procedure for the low-cost (less than $700) conversion of a Hewlett-Packard 9800 series programmable calculator for the online measurement of m.e.p.p, amplitudes. Frequency counting can also be accomplished, provided that external timing is used. Once the m.e.p.p, amplitudes are stored within the calculator, the resident statistical routines can be employed. The m.e.p.p, amplitude-measuring system consists of peak-detecting and timing circuits (Fig. 1). A preampli-
~ t M ~ ~ + I 1OK
tier must be employed such that the amplified m.e.p.p. magnitudes fall within a range from 0-1 to 9"5 V. IC1, IC2, and IC3 form a simple peak-detecting and holding circuit. IC4, IC5, and IC7 form an eventmonitoring circuit which produces a start conversion pulse when the input signal exceeds a preset threshold level (see timing diagram in Fig. 1). The falling edge of the start conversion pulse (1 ms) initiates analogue-todigital conversion of the peak value. The falling edge of the end-of-conversion pulse (400 ns minimum) sets the flag line low, signalling the calculator to read the value on its input lines. The falling edge of the end-ofconversion pulse also triggers IC6 to produce a 1 ms reset pulse to discharge the peak holding capacitor, and the system is then ready to record the next m.e.p.p, amplitude. The highest rate at which the peak detector can function is 300 per second. However, the maximum data rate is set in this configuration by the data storage rate of the
1KSV 1M
2.2K HP
+
Ol,E
START CONVERSION
9810
ENDOF fLAG
IOK
....
-15V 15F ,
10K ~
lOOK
74121
2.5K I
O
§
I
9 ~10 K
K
START ~ CONVERSION
_
_
400nsec J~l __ 1 i RESET. . . . . . . . ~/msec[ ....
ENOOF CONVERSION lr 25X
1i
CONTROL
First received5th May and in final form 1lth July 1978
i
FLAGLOW
Fig. 1 Peak detecting and timing circuits for online measurement of m.e.e.p, amplitudes.
0140-0118/79/020277 -I- 02 $01 950/0
9 IFMBE: 1979 Medical & Biological Engineering & Computing
March 1979
277
calculator, and, for the 9810A, 40 per second is the maximum.Thus, any m,e.p.p, occurring within 25 ms of a previous one will not be counted. Transient signals which overflow are converted at the maximum level, but can be rejected by the analysis program. The circuit can be adjusted to measure the peak amplitude of any pulse with a rise time greater than 1 ms by modification of the timing circuit of IC7. Low-cost 741 operational amplifiers are used for IC1 to IC5. The 74121 1-shot multivibrator is used for IC6 and IC7. The analogue-todigital converter is a Datel ADC-89A eight-bit converter. The relay is a magnetic reed relay (Magnecraft W274 DPI-2), the diodes are 1N457s. The Hewlett-Packard 9810 programmable calculator employed in this application was also equipped with an eight-bit paralM-data-transfer interface card (HP 11202A) for data storage and analysis. An eight-bit analogue-todigital converter (Datel ADC-89A) was interfaced via the H P 11202A. The total cost of this system for measuring m.e.p.p, amplitudes was $634, including $500 for the interface card, $69 for the analogue-to-digital converter, $50 for the power supplies, and $15 for the circuit components. However, this circuit is not restricted to the H P 9810, for any calculator with an eight-bit parallel interface can be employed. The system as described is currently under continuous use and provides a significant cost and time savings over hand measurements from a strip-chart recorder and at far less cost than a conventional laboratory minicomputer system (SANDERSet al., 1976; KIM and SANDERS, 1978). Although this system was originally developed for the measurement of m.e.p.p, amplitude and frequency, it can be easily modified to measure other bioelectric events such as action potentials or endplate potentials. I n any situation where a HeMett-Packard 9800 series calculator is available, the small additional cost of
278
conversion is worthwhile. However, the Hewlett-Packard calculator does have speed and memory limitations and cannot be considered a complete replacement for a minicomputer.
Acknowledgment--This work was supported in part by a centre grant from the Muscular Dystrophy Association, Inc. and N I N C D S grant NS-12905.
g. CLINTONWILKINSON NIANCHANG EDITH COBB YONG I. KIM RICHARD N. JOHNSON
Department of Neurology and Division of Biomedical Engineering, University of Virginia Medical School, Charlottesville, Va. 22901, USA
References FATT,P. and KATZ,B. (1952) Spontaneous subthreshold activity at motor nerve endings. J. Physiok, 117, 109-128. KATZ, B. (1966) Nerve, muscle, and synapse. McGrawHill, New York. KIM, Y. I. and SANDERS, D. B. (1978) Experimental autoimmune myasthenia gravis: Effects of calcium and potassium on the spontaneous release ef neurom u ~ u l a r transmitter. Exp. Neurol., 61, 311-317. SANDERS, D. B., SCHLEIFER, L. S., ELDEFRAWI, M. E., NORCROSS,N. H., and COBB, E. E. (1976) An immunologically induced defect of neuromuscular transmission in rats and rabbits. Ann. N. Y. Acad. Sci., 274, 319-336.
Medical & Biological Engineering & Computing
March 1979
