Homemade ECG machine using infrared

ecgSome interesting projects that I recently found online showed people using infrared phototransistors and op-amps to build basic light-based ECG machines. I thought that I’d try it for myself just to see how well it would work. It was certainly interesting to build this little circuit on a breadboard. Perhaps I’ll build on this design in the future, but I havn’t done so yet. The output signal is a bit noisy, but using an Arduino as an A/D converter I was able to capture my heartbeatĀ and convert it into audio using Goldwave. This design was based on a circuit posted by Scott Harden.

Bench Power Supply Part 2

Now that I’ve got my specs figured out, it’s time to start some high level design. This will allow me to get the layout of the power supply set before diving into the small details. Hopefully this will make the design process more efficient. One of the biggest things that will affect this high-level design is one particular design specification lexapro 10 mg. That is, the call for a switching knock-down stage. The reason I chose to include this is efficiency. Many lab power supplies I’ve seen out there have one thing in common: Many of them use linear regulators like the LM7805 or LM317. These are good devices, but they all have very low efficiency, especially when the dropout voltage is high. Enter switching regulators. Switching regulators can have very high efficiency (upwards of 95%) which allows for higher current handling, and less heat dissipation. However, they have a drawback. Switching regulators typically have more noise on their outputs. They may be OK for some circuitry, but this inherent noise will not do for the lab power supply I intend to build. To get the best of both worlds, I plan to use both types of regulators in my design. The switching regulator will take care of most of the voltage dropout first, while leaving about 2-3 volts for the non-switching (a.k.a. linear) portion to drop second. This will reduce power dissipated in the non-switching section of the power supply, which has numerous advantages, including (hopefully) eliminating the need for a noisy fan, as I’d like to make this thing as small, quiet, and cool as possible. This would definitely not be possible without the switching section in front. Now, it’s time to make some initial part choices:

Parts List:

Linear Output transistor: P-Channel MOSFET IRF9540
Switching Regulator: LM2679-ADJ
Switching Regulator Inductor: Digikey# 553-1121-ND
Switching Regulator Capacitor: Digikey# P15372CT-ND
Current Sensor: ACS712
This should help lay the groundwork of the power supply. Next we’ll look at putting in some control circuitry, including op-amps and so on…

Bench Power Supply Part 1

Graduation is on the horizon, and I’ve spend too many years using wall-warts as my primary bench power supplies. I’m ready to finally build something I can be proud to have on my bench. So, I’m setting out to build a really high quality bench power supply click this link here now. Every good project starts with a list of goals and in this case that means setting the specifications for my power supply. I think it’s good design practice to decide what you seek to accomplish before you spend too much time designing. So, without further delay, here are the initial specs that I’ll be designing to. Design Specifications:

Dual Floating Outputs
Adjustable Voltage, 0-30V, Steps of 10mV
Adjustable Constant Current 0-5A, Steps of 1mA
Soft output On/Off Switches (Default: OFF)
Output On/Off Indicator LEDs
OLED Text Display
Voltages/Currents set with single rotary encoder
Serial Computer Interface (Read/Set Voltage/Current)
High power efficiency, switching knock-down stage, regulated final stage
ICSP Header for firmware updates
Made from low cost parts
Now that the specs have been written down, I’ll begin designing the circuitry. Stay tuned for part 2.