Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2.
DOI: 10.17667/ iim.2016.1-2/18.
Fo ea m-a achable EMG-based wi eless con olle
Tamás Bán i BSc
Budapes Uni e si y o Technology and Economics
Facul y o Mechanical Enginee ing, Depa men o
Mecha onics, Op ics and Mechanical Enginee ing
In o ma ics
Budapes , Hunga y
ban i. [email protected]
Pe a A adi PhD
Budapes Uni e si y o Technology and Economics
Facul y o Mechanical Enginee ing, Depa men o
Mecha onics, Op ics and Mechanical Enginee ing
In o ma ics
a adi.p[email p o ec ed]
Abs ac — This pape p esen s he de elopmen p ocess
s a ing om a simple elec onic module o ampli ica ion o
EMG signals. Du ing de elopmen he asks o be sol ed we e
ex ended owa ds he c ea ion o an EMG-base con olle ha
e en ually can be connec ed o a PC. Among he main goals we e
he simplici y and low cos o p oduc ion. The e a e simila
de ices comme cially a ailable, bu he main ocus was on he
whole p ocess o design, es ing, ab ica ion and he explo a ion
o applica ion a eas. I was impo an o use medical
ecommenda ions. The de ice ma ches he sugges ion o
SENIAM, excep o he esolu ion o A/D con e sion, which is
pe missible due o he ac ha i was no designed o medical
pu poses. The inal e sion is capable o de ec ing and ampli ying
EMG signals, wi h he app op ia e il e ing and digi izing
p ocedu es o u he p ocessing. Wi h he de elopmen o
wi eless communica ion capabili ies, he de ice which can be
a ached o he o ea m can be used as a USB HID de ice wi h a
PC. A numbe o addi ional applica ions a e also discussed,
poin ing ou he ac ha his piece o echnology o e s a wide
ange o possibili ies.
Keywo ds—elec omyog aphy, a m mo emen , A duino,
STM32 mic ocon olle , signal p ocessing, USB HID con olle
I. INTRODUCTION
A. The pu pose o he wo k
Elec omyog aphy (EMG) is a widely-used medical
p ocess o examine he ac i i y o muscles. The de ice is
called elec omyog aph, he diag am being de ec ed is he
elec omyog am, which ep esen s he elec ical ac i i y o
muscles in mV o μV ange o e ime. Du ing he
measu emen elec odes a e a ached o he skin su ace o
needles a e inse ed in o he muscles. The second solu ion is
much mo e accu a e, bu i can sense he elec ic ac i i y o
jus a ew mo o uni s. This is an in asi e me hod, so medical
p o essionals use i mos ly o speci ic diagnos ic pu poses.
The nonin asi e o m is applied o mo emen de ec ion o as
a senso . The p esen ed de ice is based on he second me hod.
In o de o measu e he muscle ac i i y, a pai o elec odes is
a ached longi udinally o he skin su ace abo e he muscle.
The muscles in his applica ion a e he o ea m muscles,
esponsible o mo ing he w is and inge s. As su ace
de ec ion is he chosen me hod, he p o ound muscles canno
be examined. This is one o he easons, ha du ing
de elopmen and es ing he de ice he loca ion, o ien a ion
and unc ion o hese muscles mus be known [1], [2], [3]. To
gain mo e in o ma ion abou he a m’s mo ion, a 6 deg ee o
eedom accele ome e and gy oscope, an IMU (Ine ial
Measu emen Uni ) is used. This senso de ec s angula and
linea accele a ion. Fu he mo e, choosing he mos sui able
mic ocon olle is also an impo an s ep. I mus be able o
a end o se e al unc ions: digi izing 8 analog channels
conside ing he Nyquis -Shannon sampling heo em,
communica ing wi h he IMU and sending he da a o ano he
con olle wi elessly.
B. The cha ac e is ics o he EMG signal
Figu e 1 shows an elec omyog am measu ed by a medical
de ice. The elec odes a ached o he pa ien s’ o ea m de ec
muscles’ ac i i y while g abbing. Du ing he esea ch, he
pa ien ’s ask was o g ip a dynamome e , hen elax he
muscles. This p ocedu e had o be epea ed i e imes while
inc easing he o ce. The i s g aph ep esen s he
dynamome e ’s alues in kg, he second one shows he aw-,
he hi d one he il e ed EMG signals in mV, all o hem o e
ime.
Fig. 1. Elec omyog am [7]
I can be easily obse ed ha EMG signals a y, while he
g abbing o ce is cons an . Acco ding o he en elopes, i
would be eally di icul o de e mine he ix g abbing o ce.
Ano he obse a ion is ha he huge o ce one exe s, he
highe he g aph’s g adien is. This e ec is explained by he
s ia ed muscles’ a igue. Mo eo e , he en elope’s
smoo hness can be inc eased by educing he low-pass il e ’s
equency. Howe e , his would wo sen he eac ion ime.
Las , bu no leas , i is a di icul ask o di e en ia e low-
o ce g abbing signals om noise.
Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2.
DOI: 10.17667/ iim.2016.1-2/18.
Summing up he consequences o he measu emen , i is
clea ha du ing he p ocessing o EMG signals, one has o
deal wi h se e al di icul ies.
II. HARDWARE INTERFACE
A. Designing and building he ci cui
I was necessa y o design and build a ci cui o
measu ing and ampli ying he EMG signals. A i s , a es -
panel was buil o he de ec ion o only one EMG channel,
based on ideas om [8]. A common A duino panel was used
o digi iza ion o he measu ed EMG signal. Gaining
expe ience om his unc ioning ci cui , he inal panel, which
can measu e 8 channels was designed and c ea ed. I con ains
an accele ome e and gy oscope, as well as a wi eless adio
module. The A/D con e sion o signals was pe o med by an
STM32F4 Disco e y panel, because i s speed and esolu ion
a e much highe , han ha o he i s choice o A duino Mega.
The ol age supply was a 9V ba e y.
B. The panels in he de ice
The de eloped panels can be di ided in o wo g oups
based on hei unc ions: ins umen a ion ampli ie panels and
ope a ional ampli ie panel. The second one is also a shield o
he STM32. The ins umen a ion ampli ie de ec s he
po en ial di e ence be ween he wo ends o he muscle ha is
how he EMG signal is gene a ed. Mo eo e , hese panels
p o ide ampli ica ion by 20. As i ope a es om an
asymme ic powe supply, he signals ha e o be pu on o a 1,5
V o se be ween 0 and 3V. Then a band-pass il e was
applied, which emo es he unnecessa y high and low
equency componen s. By cu ing he low band, he d i and
he DC o se a e elimina ed. High- equency il e ing ex ac s
he noises and p e en s aliasing. Acco ding o SENIAM
(Su ace Elec oMyoG aphy o he Non-In asi e Assessmen
o Muscles) [5], o su ace elec odes 5-10 Hz high-passing
and 500 Hz low-passing should be used (Figu e 2). In he
cou se o he de elopmen , based on he ga he ed da a, 7.23
Hz high- and 482.29 Hz low-passing equencies we e se .
Fig. 2. Schema ic ou line o a sEMG eco ding sys em [6]
C. The inal PCBs
A e planning he ci cui s, NI Mul isim simula ion
so wa e we e used o es s. Figu e 3 shows he Bode diag am
esul s om he simula ion.
Fig. 3. Bode diag am esul o he simula ion
The PCBs we e designed wi h a p og am called DipT ace.
PCB e ching and solde ing he componen s we e he inal
manu ac u ing s eps. All in all, 8 smalle panel (Figu es 4 and
5), as well as a la ge shield we e made (Figu es 6 and 7).
Fig. 4. PCB design o he small ins umen a ion ampli ie ’s’ panel
Fig. 5. PCB o he small ins umen a ion ampli ie ’s’ panel
Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2.
DOI: 10.17667/ iim.2016.1-2/18.
Fig. 6. PCB design o he shield
Fig.7. PCB o he shield wi h he ope a ional ampli ie s, he wi eless adio
module and he IMU
III. SOFTWARE INTERFACE
Fo he compu e p ocessing o he signal, a digi al low-
pass il e is needed because o he i ing o he en elope.
Fi s , he signal mus be ec i ied: he p og am measu es he
EMG signals symme ic o 1.5V, hen subs ac s he mean
alue om hem, so ha he o se will be 0. A e ha
nega i e numbe s will be in e ed. As o he il e ype, he
usage o IIR (In ini e Impulse Response) is easonable,
because i p o ides highe p ocessing speed and esul s in a
smoo he en elope, han FIR (Fini e Impulse Response)
il e s. A 2nd o de Bu e wo h il e wi h 5 Hz cu was
chosen a e ex ensi e es ing.
A. Tes ing
The boa d was es ed wi h an A duino Mega a i s . To
display he signals, a ba e y-powe ed lap op was chosen, in
o de o elimina e mains dis u bance. The p og am sen he
aw and he il e ed EMG signals wi h se ial communica ion
o he PC, whe e hey we e eco ded. These esul s we e
isualized wi h Mic oso Excel. Figu e 8 shows he aw
(uppe ) and he il e ed (lowe ) EMG signals using 5 Hz cu .
The ho izon al axis shows ime in seconds, he e ical axis
shows he digi ized alue, whe e 1023 bi co esponds o 5V.
Fig. 8. The aw (uppe diag am) and he il e ed (lowe diag am) EMG signals
using 5 Hz cu
B. Final boa d
The inal de ice unc ions (Figu e 9) as a con olle
a ached wi elessly o a PC. I is able o handle 8 di e en
EMG signals and he da a o he IMU simul aneously. The
ci cui s a e loca ed in di e en plas ic boxes, which can be
a ached o he o ea m wi h an elas ic band. The STM32 and
i s shield a e in a bigge box. The nRF24L01+ communica ion
module p o ides he high ange wi eless communica ion wi h
he PC.
Fi s , he ansmi e p og am eads he signals o he 8
analog inpu s. Each o hem a e a e aged, o ming he
channels’ o se s. O se s a e sub ac ed om aw signals, so
hei mean alue will be 0. Nega i e signals a e in e ed, hen
a 2nd o de Bu e wo h il e p ocesses hem. These signals
and he IMU’s da a a e sen o he ecei e .
The da a a i e in an a ay o he ecei e , which
disassembles and pu s hem o di e en a iables. The
ecei e con e s IMU’s da a in o he i ems o X and Y axes.
Two EMG signals, gene a ed by a lexo and an ex enso
muscle, a e u ned in o a logical alue. I he muscle is ac i e,
a bu on is pushed. All he da a a e sha ed wi h he PC.
Fig. 9. The inal de ice
Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2.
DOI: 10.17667/ iim.2016.1-2/18.
IV. CONCLUSION
The i s expe imen al esul s came om es ing he panel
made o A duino. A e ha a p in ed ci cui boa d was
designed, buil and es ed, so ha inciden al e o s could be
ecognized and co ec ed. Then he digi al il e s app op ia e
o adjus ing he en elope we e selec ed. La e on he inal
de ice was made "mobile" wi h a 433 MHz communica ion
module. Du ing he p ojec , he e o s we e iden i ied and
co ec ed, so ha in he inal de ice hey we e omi ed.
Wi h he expe ience gained du ing de elopmen and
es ing, a much as e sys em was designed and c ea ed, ha is
capable o moni o ing 8 muscles, and can be placed on he
o ea m wi hou elec ode cables. STM32F4-Disco e y
handles digi iza ion, and includes a much as e
mic ocon olle han A duino, so ha he sampling equency
could ha e been inc eased. Fu he ad an age o STM32F4-
Disco e y is a 12 bi A/D con e e compa ed o A duino's 10
bi sys em, inc easing he esolu ion o he sampled signals.
Choosing he new, high pe o mance 2.4 GHz wi eless
communica ion ins ead o he 433MHz modules, he
ope a ional ange and da a speed inc eased conside ably. By
upg ading he de ice wi h a Six-Axis Mo ion T acking
De ice, he a m's posi ion and mo emen could be moni o ed
wi h mo e de ails. The ci cui boa d o he ecei e , which is
able o communica e se ially wi h he compu e was also
designed and buil . Fu he mo e, he inal de ice can be
connec ed o he compu e as an USB HID (Human In e ace
De ice). The e is no need o ins all a d i e , he de ice can be
used soon a e connec ion. This unc ion was es ed on a
ocke powe ed ai c a simula o game called HAWX, whe e
he igh e je s we e con olled by he de ice a ached o he
playe 's o ea m (Figu e 10).
Fig. 10. Playing wi h he simula o
V. FURTHER APPLICATION AND TASKS
A. Examina ion o muscle a igue
The o ea m muscles a e olun a ily mo eable s ia ed
muscles, which a e p one o a igue. This ea u e can be
de ec ed wi h an EMG boa d. All one has o do is o pu he
elec odes on o he biceps muscle. Then a hea ie weigh
should be li ed and hold as long as possible. Du ing he
exe cise he ampli ude o he EMG signal educes slowly. I is
also a good idea o use he de ice o wo kou ollow-up.
B. Follow-up o physio he apy ea men s
When someone needs o do physio he apy egula ly, he
e iciency could be supe ised, as well as he buildup o
s eng h. Fo ins ance, du ing he exe cise he pa ien should
epea edly push a small ubbe ball. The mic ocon olle
coun s one up a e he EMG signal eaches a ce ain analog
alue.
C. Con olling a d one o mobile obo
The 2,4 GHz communica ion module can be used o
con ol d ones o e en obo s because o i s qui e la ge ange.
Mo ing he gy oscope, i can di ec he con olled ehicle’s
mo emen . Wi h he s e ching o elaxing o muscles
di e en o de s can be gi en. One o i s ad an ages is ha he
hand emains ee.
D. Examining walk and balance
The inal de ice shows muscles’ elec ic ac i i y in a
sui able way, so a aching i o he leg, he ac i a ion le el can
be sensed while walking o balancing.
E. Redesign
I is wo h o examine he possibili ies o edesign he
de ice in a mo e compac o ma , o a wide ange o
applica ions.
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