# Title Team Members TA Documents Sponsor
8 Isolated Guitar Pedal Power Supply
Abigail Kokal
Connie Yun
Dearborn Plys
Jialiang Zhang design_document1.pdf
# **Isolated guitar pedal power supply**

Team members:
- Connie Yun (csyun2)
- Abigail Kokal (arkokal2)
- Dearborn Plys (dplys2)


Guitar players and other instrumentalists often use audio effect boxes, usually referred to just as guitar pedals. These pedals require supply generally at 9V, 12V, or 15V with current ratings usually from 100mA up to 1000mA (in the case of some digital effects units). "Clean power" is the major requirement in these supplies, this means decoupling from AC sources and minimization of noise. Supplies for these pedals also need to have many outputs, as many pedal boards (collections of pedals used in series for one audio signal), have a number of individual units all requiring their own power. Most pedal power supplies on the market are quite expensive, don't always supply the exact combination of required output voltages, and don't have options to vary the output voltages for stylistic purposes. Stylistic variation in supply voltage refers to underpowering, and is used often by effects units to vary normal operation of external effect units. This power “sag” function mimics supply from a dying 9V battery.


The isolated power supply would plug into the wall, which would mean that we would have to work with AC/DC conversion, as well as output 9, 12 and 15 V on different ports, which would involve DC/DC conversion. The microcontroller would be used to control switches in the DC/DC converter, and while this kind of item exists online, we would want to make it more precise in terms of ripple, and with the option of purposeful undersupplying voltage for stylistic purposes. Isolation in this case would involve both isolation from noise, which is where ripple precision comes in, and of power, where we would potentially implement a transformer. While we also have the idea to make this have the option of being battery powered as well, this would likely be more of a stretch goal than anything else.

# **Solution Components**

**Subsystem 1**
AC/DC converter. The AC/DC converter would be based on a bridge rectifier, adjusting the overall schematic as needed. This would include a transformer, diodes, and then some filtering components. This would bring us from an outlet to the DC power that we work with for the power output. This would go from the AC voltage of 120V from the wall down to 3V.

**Subsystem 2**
Isolated DC/DC converter. The goal is to essentially create two three-winding transformers, with the outputs equating to as close to 9V & 12V, and 15V & 18V as possible. In this case we will be stepping up from the 3V output from the AC/DC converter. The schematic would be based on a flyback converter, with necessary changes added as they come up. The microcontroller in this subsystem would be used for controlling the switches needed to run the converter.
For this subsystem we would likely only need items that can be found in the electronics shop available to the students, such as copper wire, a core, capacitors, resistors, diodes, inductors, as well as switches. Further specifications will be calculated once the shop is visited and available stock is observed. Proposed switch: IRFP450

**Subsystem 3**
Undersupply of voltage. Mimics a dying 9V battery for stylistic purposes. This would be an option for the 9V output, where we can use the microcontroller to control the level of undersupplying happening. We can implement some sort of nob or slider to control the corresponding voltage level. This would likely involve a transformer in combination with a controlled variable resistor.

**(Stretch Goal) Subsystem 4**
This is something that we would look into further, if we think we have time for it down the line, but essentially the idea would be that you could disconnect the AC/DC converter from the rest of the system and attach the battery.

# **Criterion For Success**
- Output ports supply at DC with under 5% output ripple
- Undersupply “sag” output responds to user choice between 2V and 9V
- Have 4 working ports for output voltage at 9V (with sag option), 12V, 15V, 18V
- Stretch goal: Option to have it run on battery [optional]

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The purpose is to create an inexpensive growing degree day monitor that records temperature and computes growing degree days for a specific farming field during a growing season. This monitor will be placed near a farm field where it will monitor temperature conditions during the growing season. It will record both the ambient air and soil temperatures over the course of day. These temperatures will then be used to calculate the growing degree days. The cumulative number of degree days will then be displayed on either a seven-segment display or this can be downloaded to a computer. This monitor will be powered through a combination of both solar and battery power.