Volume Measurement Research Update

1. Volume Measurement Research Update Sukhi Basati PhD Candidate Laboratory for Product and Process Design Director: Andreas Linninger, PhD 8/25/2010

3. + µC actuator - sensor Research Outline An Implantable System for Intracranial Volume Measurements in Hydrocephalus • Translational Research • Device can be designed with existing shunts • Catheter with ring electrodes • Designed as sleeve to fit around shunt catheter • Towards active control of Hydrocephalus • Feedback control of ventricular volume • Active vs. passive control systems • Simpler devices, less malfunction? • Addition of pressure transducers • New knowledge gained • Continuous measurements of volume • Can we validate p-v relationship • Future Studies on Tissue Compliance • Age dependence Show microelectronic unit from prelim

4. Sine wave oscillator Variable amp. Voltage to Current Converter Microelectronic Design • Requirements • AC signal excitation • Constant current • High SNR • Data acquisition Instrumentation Sensor Resistor Power Brain (phantom) Inst. Amp G = Variable • Advantages • Adjustable current source • Adjustable frequency • Adjustable gain • Modifiable design • MCU integration Microcontroller (Power control + Digital signal out to RF transmitter) RMS – DC Converter Testing of instrumentation with decade box Characteristics with Resistor Decade Box

5. Wireless demonstration with analog-digital conversion

6. 1. Program LED on-off and put to sleep • 2. Analog-Digital Conversion • Store data in 8-bit register 3. Serial Data Communication Methodology How did I reach this milestone? void main() { //initialization TRISIO = 0b101110; //configure GP0 and GP4 as output OPTION = 0b11001111; //set WDT timeout: prescaler assigned to WDT (PSA=1) // WDT timeout = 2.3 s CMCON0 = 7; //disable comparators ANSEL = 0b00010100; //GP2 is only analog (pin 5) ADCON0 = 0b00001001; // in ANSEL, put 001 in ADCS<2:0> bit for conversion clock //put in ADCON0 register CHS<1:0> : read from AN2: 10 // in ADCON0 change ADFM (bit 7) to left justified : 0 // so most significant eight bits of data is in ADRESH // change VCFG (bit 6) in ADCON0 (reference voltage) to 0 // and change ADON to 1 in (bit 0) of ADCON0 register // so ADCON0 should look like: 00001001 for (;;) { LED1 = 1; delay_ms(4); GODONE = 1; //start conversion while (GODONE) //wait until done ; synch_out(85); delay_ms(1); ser_out(ADRESH); LED1 = 0; delay_ms(12); } } Steps taken to reach objective:

7. 0 Start bit Brief Explanation of Serial Data Communication using RS-232 Protocol • Very old protocol, much more advanced wireless systems exist today. • Who cares? • Receiver and Transmitter must “talk” to each other. • Both are 434 Mhz RF transmitters. (okay for animal testing) • The transmitter emits a synchronization byte (8 bits) followed by a brief delay, and then the register with the analog-digital converted values (8 bits) is sent. transmitter 0 1 0 1 0 1 0 1 0 Receiver looks for “U” then records any data after the start bit Start bit Data (8 bits) Synch bit Reads: 01010101 Decimal for 85, character value of “U” (see ASCII table)

8. Future Goals • Include Battery, and include sleep mode with microcontroller. • Also need to consider some sort of battery clip to PCB, and a metallic case enclosure to also act as an antenna. • Test device for long term (1 day, week, month). • Scale down instrumentation on printed circuit board. • First using through-hole components, then ultimately designed a surface mount PCB. • Additional sensors can be easily integrated with microcontroller (still have 3 A/D ports). • Fabricate additional sensors (large, small) and test with new electronics. • Coat sensors in parylene. • Test in acute rat HC model.

9. Proposed Fall 2010 Plans • Submit Rat HC Measurement Paper to JNS-Pediatrics • Priority: Medium • Fabricate Microelectronic Unit for Long Term Measurements • Priority: High • Perform Sensor Simulations (Positional Dependence) • Priority: Medium • Submit Grant • Priority: High