Jacob is currently studying the formation of soot in engines using molecular dynamics and quantum chemistry to look at gas-soot interactions and self-assembly processes within carbon materials. He uses physical models and simulations to describe the chemical world and is developing instruments to measure chemical properties. Jacob has strong interests in renewable energy, pollution reduction and carbon nanomaterials. This included research in the areas of ultrafast spectroscopy, Raman spectroscopy, Bayesian data analysis, computational chemistry and microfluidics. He completed a Bachelor of Science with First Class Honours in Chemistry and Physics followed by Masters in Chemistry at the University of Auckland (New Zealand). Jacob is a PhD student in the CoMo group and a member of Churchill College, University of Cambridge. SPI.transfer(200) //transfer the byte that sets the valueĭigitalWrite(Dselect, HIGH) //Turn on the correct PinMode (Aselect, OUTPUT) //Set pins as outputsĭigitalWrite (Aselect, LOW) //Write high or low digital value to pinsĭigitalWrite(10, LOW) //Set the chip select for the first pot To put it simply, I did not plan for it in the design so I used a circuit which had built-in impedance. There are other things to take into account, like reflection caused by ill-matched impedance. This leads to no trailing of the pulse as the current is quickly removed, however this requires that enough current is outputted current to keep the voltage above the triggering threshold. In a lot of high speed systems impedance (another way of thinking about resistance if taken in the context of DC circuits) is very low. However, this usually leads to a voltage drop due to the load this resistor places on the circuit. Using drop down resistors from the signal line to ground it gives the current a place to quickly discharge. As I understand it (and you can test this yourself) a lot of electronics have a long decay after a pulse has passed through due to the current having nowhere to discharge. The impedance was not taken into account and a simple signal generator was used to provide the needed current for the high speed electronics which uses input impedances of 50 Ohms. Finally, the pulse is lengthened in a fixed delay, giving the laser the right pulse length for it to trigger. The output pulse then triggers the next timer, which has a PCB mounted pot for referencing between the lasers. The first two have four delays which are variable between 4 ns to 10 ms by using four different capacitor values and 100kOhm variable resistors. This gives the delay time in seconds as the product of the resistor and capacitor values. When the voltage in the capacitor is 66% the output pulse is toggled low. This discharges the capacitor and then charges it again. When a pulse is detected the output becomes high via a Schmitt trigger. These chips used two timers whose time constants were determined through a capacitor and resistor. The delay was set up using monostable multivibrator chips (TC74HC123(F) $NZ1.56).
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