1. Baby MIND Collaboration Meeting #2
LED Driver
Georgi Mitev

2. Initial LED driver design and use
Single channel design
16 amplitude levels
50ns min pulse width
Onboard LED, modified to work with external LED
RS-232
interface
Manual control and mode display
MCU
LED driver
amplitude
timing 1

3. Pulse Shape 2 200 ns pulse 50 ns pulse
200 ns pulse, fed to LEDs over 2m coax
50 ns pulse, fed to LEDs over 2m coax 2

4. Master timing control unit
Upgraded LED driver
Oscilloscope
Optical Pulse Control unit
Optical pulse feedback
Timing pulse channel 1, 2 & 3
LED tube & fiber bundle coupling
3- channel amplitude control unit
Optical fiber bundle
Amplitude control bus I2C
Onboard USB & WiFi to RS-232 bridges
Master timing control unit 3

5. LED driver modules block diagrams
To the remote addressable LED probes
Local control and display
dsPIC33EP64GS504
Wi-Fi module
ESP8266
USB - UART
FT232RL
Real Clock
DS1307
Non-volatile memory FM24VN10
SCI1
SCI2
I2C 2
Control measurement circuit
I2C 1
PULSE1 & PULSE2
control
Chanel 1
Chanel 2
Chanel 3
MS0
MS1
ADC T1
LMH6559 buffer
Power control
MUX
I2C buffer
Round board - interface and signal distribution
PULSE
From the Main unit
I2C
Addr. Sel.
I2C - PIO
Level translator
DAC1
DAC2
DAC3
LED Driver 1
LED Driver 2
LED Driver 3
Current mirror
Current mirror
Current mirror
LED1
LED2
LED1
BLUE
GREEN
RED
Rectangular boards – LED driver
I2C
Pulse
I2C
Pulse
I2C
Pulse
System controller block diagram
LED tube unit block diagram 4

6. Light output measurements with PIN diode
Some signal is observed on the PIN diode (green trace 4), but it’s hard to observe any signal parameters due to the noise.
It can be seen that the light emission starts and stops immediately with the current flowing through the LED.
It was determined that the aluminium foil, used to wrap the LED & PIN setup, is acting as a wave guide and is channeling the electrical noise from the LED to the PIN diode.
Trace 1 – 30ns timing pulse
Trace 2 – LED current
Trace 3 – LED voltage
Trace 4 – PIN diode output 5

7. Light output measurements with SiPM
Measured output increases to between 10 and 50 p.e.
Timing pulse width = 15.8 ns, maximum amplitude 6

8. Current state of the new LED driverP W A
Pulse Output 1
Pulse Output 2
Separately controlled
T – period (65.5μs)*
P – phase/delay*
W – width(8ns)*
A – amplitude (32 levels)
*in 1ns steps
Hardware – 4 sets
Controller
LED torch boards assembly x2
SMA timing cables x2
USB A – USB B cables x3
LED torch tube & fiber bundle x2
Firmware
Basic pulse parameters control
Advanced pulse control (pulse packets, longer period)
Onboard measurement circuit
Communication protocol
Control Interface
Terminal program
GUI program
Development status
- complete - incomplete - not started 7

9. Bar tests The LED driver is used to test the bar WLS fiber.
All bars currently in the dark room have been tested. 8

10. Bar tests
Due to lack of optical fiber bundles for the new LED system an alternative setup is used for testing. One of the new LED drivers is modified to output the pulse on an SMA connector. A short cable is used to connect it to the old fiber bundle.
Current test experience – it takes min. to test 32 horizontal bars. Most of the time goes into handling the bars. 9

11. Half module tests
Module assembly, module testing and bar testing can go in parallel.
Once a half module is assembled it can be tested quickly with the LED system.
The possible test setups are being evaluated. 10

12. Conclusions The new LED system has been developed and tested.
Four sets have been delivered to Geneva.
It has been used to test the currently available scintillating bars.
A GUI application is under development. 11