# Electronics 101

Hi Makers!

I prepared an "Electronics 101" presentation for Biomechatronics in my first semester. I believe this can be relevant for you guys. The topics are:

• Units
• Ohm and Kirchhoff
• Series and // resistors
• Resistive divider, LED current limiter
• Operational amplifiers
• Passive filters
• BJT Basics
• MOSFET Basics
• High-side vs Low-side switch
• MOSFET, BJT or Relay?
• Voltage regulators
• Thermal
• ESD
• LiPo Batteries
• Misc. tips, breaking some myths
• Useful tools

You can get the slides here : Electronics 101

I used PowerPoint 2013 on a PC. Linux has trouble viewing the files in LibreOffice (weird background) but you can use the web-based Office to view the slides.

# FAQ

I will keep this section up to date with your (anonymized) questions.

Q:Does the voltage divider (with two resistors) always provide the same voltage drop, regardless of the load/resistance on V_OUT? I suppose not, so how do we regulate this?
A 1):No. The rule of thumb here is to load the circuit with 10-20x more resistance. If you make your divider with 10k & 10k you shouldn't connect it to a load lower than say 100k.
A 2):Please note that even 10k & 10k is high for an ADC input. A cheap & simple trick is to place a small (say 10 or 100nF) cap in // with the lower resistor.
A 3):To keep this voltage independent of the load use a follower opamp

Q:If you need to drive a very large motor (PWM) with MOSFETs, can you use them in parallel? Anything to be aware of in this case?
A:Yes, you can. That's a common practice. Always use 1 gate resistor per MOSFET and make sure that your gate driver can provide enough current for all the gates.

Q:What do we need to be aware of when charging and discharging LiPo packs to avoid fires? Isnâ€™t LiPo charging circuitry usually pretty complex? (Voltage monitoring, reduced current as it reaches capacity, etc.)
A:Short answer: use a specialized IC or an off the shelf charger. There is plenty of chips that will deal with the charge and discharge for you. Never plug a LiPo to your circuit if it doesn't have a protection circuit (a lot of them have a tiny under voltage cutoff circuit soldered near the leads)

Q:Do we need 1 resistor per LED in parallel because otherwise, the current flow will be much higher in some LEDs than others (due to manufacturing variances, etc)? Or for some other reason?
A 1):Yes. If you look at the Current/Voltage curve of a diode (http://www.amperor.com/products/led/images/led_i_v_curve.jpg) you'll see that a slight voltage difference can create a huge difference in current.
A 2):What will happen if you // LEDs with only 1 resistor is that you'll destroy the one with the lowest voltage... then the second lowest... up to the point where they'll all be dead

Feel free to contact me at jfduval (at) mit (dot) edu if you have any questions or comments!