New LED driver Preliminary tests G. Mitev, E. Noah 1st September 2016

Master timing control unit New LED driver Oscilloscope Optical Pulse Control unit Timing pulse channel 1, 2 & 3 Optical pulse feedback 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

LED driver modules block diagram 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

Test goals Preliminary tests explore light pulse characteristics of NEW LED driver compare with old LED driver

NEW LED “Torch” setup “LED driver controller” controlled manually from push buttons installed on the module (i.e. not connected to a PC). sends “timing pulse” to LED driver. One LED interface board “round board”. One LED driver board “rectangular board” with one high brightness LED installed on it.

PIN diode light output measurements 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 (inside the red heat-shrink tube), 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

PIN diode light output measurements The aluminium foil was removed and the coupling between the PIN and the LED was much worse. The observed signal is much cleaner. The PIN signal clearly has 2 regions with different slopes, raising the question for their origins. Trace 1 – 250ns timing pulse Trace 2 – LED voltage Trace 3 – PIN diode output

Noise issues with first tests We connected a Hamamatsu S5973 photodiode to one ADVANSID amplifier board (ASD-EP-EB-N), and brought the diode in contact with the LED. Lots of noise was observed on the diode signal. This noise is actually electrical noise originating from the LED driver “rectangular” board. Changed setup: LED to one connector of rectangular scintillator slab with WLS, MPPC S12571-025C to other side of connector.

MPPC S12571-025C: Dark noise One photo-electron corresponds to ~50 mV

Timing pulse width = 14.8 ns This is the minimum timing pulse width that leads to a measurable output on the MPPC Amplitude set to maximum: both in software, ... and with the potentiometer on the hardware rectangular LED carrier board

Timing pulse width = 15.8 ns Measured output increases to between 10 and 50 p.e.

Timing pulse width = 16.9 ns

Timing pulse width = 17.8 ns

Old LED driver: Pulse train mode Settings required for measureable light output at MPPC Pulse train mode (max. freq. = 10 Hz): Amplitude setting: 6 Pulse width setting: 200ns Pulse period setting: 127 ms Note: a fiber bundle was used for these tests

Old LED driver: hardware mode Settings required for measureable light output at MPPC Hardware mode (min freq. = 20 kHz): Amplitude setting: 11 Pulse width setting: 400ns Pulse period setting: 127 ms