3D Printing A Banana Pi Box

Many of our customers purchase supplies from our store in order to build 3D printers. This inspired us to build our own 3D printer a few months ago using stepper motors and the various other components required. After printing other people’s designs from www.thingiverse.com using our 3D printer filament for our first few prints, we decided it was time to create one of our own.

Inspired by some of the other Banana Pi boxes we found on Thingiverse, we chose to print a plastic box for our quad-core Banana Pi M2 single-board computer with built-in WiFi.  Frist, we sketched up the snap-together box using Google Sketchup.


Once the six sides of the box were sketched as .skp files, we had to convert them to .stl in order to share them on Thingiverse and so we could eventually convert them into a file for our 3D printer. We used an extension in Sketchup to export the .skp as an .stl and subsequently converted this file into .gcode (using Skeinforge), so our Mendel90 3D printer could print this file.


Although the final print was accurate to the CAD files, we noticed a few issues. The box was slightly too small to envelope the Banana Pi M2 and the holes where the sides fit together were a bit too snug. We will revise the drawings by increasing the scale by about 1-2% and give it another go! You can find the current .stl files here on Thingiverse. Keep an eye out for a future update, after we revise the design.

IMG_7846 IMG_7848



Testing Batteries with a DC Electronic Load


Because energy efficiency and reliability are important design criteria in most applications in today’s battery-intensive environment, it is important to use suitable test equipment capable of accurately measuring and displaying the results that define the performance of the batteries under test.

This is becoming a very intense area for research and development as products such as electric vehicles, 4G cellular phones, portable computers, and battery-powered drones become prevalent in modern society.

A popular device to accomplish this testing is a programmable DC electronic load, which will help you test various settings, configurations, schemes, and methodologies. This article concerns using a DC electronic load to test batteries.


Testing batteries under load is the optimal method for determining energy efficiency and battery lifetime. This reflects the energy efficiency of the battery power source. A standard test of performance consists of analyzing the discharge curves that represent the performance characteristics of the battery source under the conditions defined by the programmable DC load. Observing these curves allows the engineer to measure the battery life and compute the battery’s efficiency.

Some DC loads provide this feature to provide battery discharge measurements. The total charge is provided in Ah (Amp-Hours) to a specified voltage. Several of the  programmable DC electronic loads available from Circuit Specialists provide this useful built-in function, which enables you to quickly set up and test. Below is a description of a simple discharge test designed for testing consumer-grade “AA” sized batteries. This example can be applied to a wide variety of other battery types and configurations.


Step one is to connect the battery being tested to your electronic load. Both soldering wires to the battery or using a battery holder will work. You may use the software provided by the manufacturer of the programmable load or write a custom program using LabVIEW or SCPI commands so they can save the data points in real-time when the test cycle begins. Ensure that you have a suitable connection to your PC using an RS232 or USB cable.

DC Load Setup

The setup of the DC electronic load testing the battery is controlled by the software program. Be sure to manually set the voltage and current range before running the test program. If the current is quite large, you may want to use the remote voltage sensing feature of the DC load


The plot shown below is a simple example of the battery discharge curve for a consumer-grade “AA” alkaline battery tested with a DC programmable electronic load. This test was completed in constant current (c.c) mode with a ½ amp load and a cutoff voltage of 0.5 volts. If you look at the discharge curve, you can determine and analyze the behaviour of the battery and the battery’s capacity under this loading condition.

Wireless Arduino control of a large NEMA 34 stepper motor

Learn how to drive a large NEMA34 stepper motor using one of our motor drivers, a 12V power supply and an OSEPP R3 Uno controller running Arduino software.

4 CH RF remote control system provides wireless control: RXD4140-434 schematicImg4

Arduino code:

#include <Stepper.h>

int sensorPot = A0;
int sensorValue = 0;
int forward = 2;
int reverse = 3;

void setup() {
pinMode(8, OUTPUT); //direction pin
pinMode(9, OUTPUT); //step pin
digitalWrite(8, LOW);
digitalWrite(9, LOW);

void loop() {
sensorValue = analogRead(sensorPot);
sensorValue = map(sensorValue, 0, 1023, 3600, 1);

int f = digitalRead(forward);
int r = digitalRead(reverse);
if(f == 1 && r == 0){
digitalWrite(8, LOW);
digitalWrite(9, HIGH);
digitalWrite(9, LOW);
if(r == 1 && f== 0){
digitalWrite(8, HIGH);
digitalWrite(9, HIGH);
digitalWrite(9, LOW);

Basics of Electronic DC Loads

To select a DC electronic load that best fits your desired application, you should first consider the task or tasks that the load is going to be used for.

Some things to consider when selecting an electronic load are:

  • What are the lowest & highest voltage points that you need the DC electronic load to read?
  • What kind of measurements are needed (RMS measurements, digitized, etc.)?
  • What is the highest current operating point that the electronic load may need to read?
  • Will the electronic load be testing one unit per test or will you need to test several units?
  • Does the DC electronic load have front panel connections? This may be critical to reduce cable drop and increase the accuracy of the electronic load.
  • Can your electronic load be quickly reconfigured for changing applications?

Once you have determined which tests you need to perform, you will be ready to select the right DC electronic load. The four major modes of operation for an electronic load are constant current (CV), constant voltage (CV), constant resistance (CR), and constant power (CP).

A well-designed electronic load will always control the current. No matter what mode the load is in, it is always controlling the current, which will allow you to set a current level that the DC load will draw regardless of any changes in voltage.

Constant resistance (CR) mode allows you to set the resistance value. The load will then adjust the current draw inversely to compensate for any change to the testing voltage. Constant voltage (CV) mode allows you to set a fixed voltage. The electronic load will sink the necessary current to keep the voltage at the set level. Constant power (CP) mode allows you to set the wattage level required for your test, and then the load will adjust the current draw proportionately to compensate for any changes in the voltage. These settings will remain constant, unless there is an event that triggers one of the protection modes.

DC electronic loads typically include standard PC interface features including RS-232 and USB (GPIB may also be provided). Using your computer to control and record testing data through an electronic load can help you set the DC load’s control parameters as well as record all events that occur during the testing period.

The Banana PI BPI-M2 as a ADS-B radio receiver controller


The Banana PI BPI-M2 makes a great base for an aircraft data receiver station for ADS-B transmissions. ADS-B (Automatic Dependent Surveillance – broadcast) is the new standard for aircraft position reporting worldwide and most aircraft use it to send their position to ground controllers and other aircraft. There are several websites that show aircraft in flight worldwide. These websites receive their aircraft data in many ways and the radio hobbyist is one of them.


To receive the 1090 MHz ADS-B radio signal requires a capable receiver and antenna as well as a computer to process the signals and plot the locations. The Banana Pi BPI-M2 is a capable computer for this task. We coupled it along with a small inexpensive USB powered radio receiver called a DVB-T stick to receive the 1090 MHz signal.

An external rooftop antenna is desirable for best reception, but we are using the small antenna supplied with the DVB-T receiver for this blog article.


We are sending data to FlightRadar24.com for this example, but the setup is similar for the other sites out there. FlightRadar24 has a software package and instructions for the Raspberry Pi system and the Banana PI BPI-M2 will run the same Rasbian operating system so setup is fairly easy.


The needed items are as follows:

  1. Banana Pi BPI-M2 computer board
  2. The Raspbian operating System
  3. 5 Volt @ 2 Amp power supply (Either micro USB or one with a 4.0×1.7mm barrel connector.
  4. USB DVT-B receiver module and antenna
  5. Powered USB Hub
  6. 4GB or larger Micro SD Card

The DVB-T receiver draws enough power that the powered USB hub is recommended so that the ports on the Banana Pi are not overloaded.

Once you have all the needed components you will need to follow the installation instructions to setup and install the Rasbian operating system as well as the FlightRadar24 software. It is all command line based, but pretty well documented.

New 19″ Rack Mount for Array Power Supplies & Electronic Loads

Circuit Specialists now stocks a rack mounting kit for the Array 3600 & 3700 series power supplies and electronic loads. The Array 19″ rack mount kit allows for a convenient mount into a standard 19 inch rack.

You can mount either one


or two


of the Array units on the mount.

The following Array power supplies and electronic loads are compatible with the Array 19″ rack mount kit:

Power Supplies

CSI3644A Programmable Power Supply 0-18V / 0-5A

CSI3645A Programmable Power Supply 0-36V / 0-3A

CSI3646A Programmable Power Supply 0-72V / 0-1.5A

Array 3662A Programmable Power Supply 0-35V / 0-14.5A

Array 3663A Programmable Power Supply 0-80V / 0-6.5A

Array 3664A Programmable Power Supply 0-120V / 0-4.2A

Electronic Loads

CSI3710A Programmable Electronic Load 360V / 150W

CSI3711A Programmable Electronic Load 360V / 300W

Array 3720A DC Electronic Load

Array 3721A Programmable DC Electronic Load 0-80V / 0-40A

Array 3722A Electronic Load

Array 3723A Electronic Load

The Array 19″ rack mount kit provides you with a very professional looking rack mount solution designed specially for reliable Array power supplies and electronic loads.


How to Install Windows 7 & 8 drivers for the Hantek 365B Data Logging Digital Multimeter

The auto-install program supplied on the disk included with the Hantek 365 USB Data Logger can be confusing for some users when they attempt to load the drivers for Windows 7 or 8. This blog is intended to show you how to install the drivers if you’re having trouble.

The drivers are provided on the supplied disk in the Drivers sub-directory and are labelled as “Hantek DMM“. Step 1 is to use the auto-install program on the disk to install these drivers. To do this, you may need to manually update the drivers via the “Control Panel System” settings in Windows.

Go to “Control Panel Device Manager” and expand “Universal Serial Bus Controllers“. There you will find a device listed as “ST Micro“. Click on this device (i.e. ST Micro) and select the option to “Update Driver” and then select the option to “Let Me Choose the Driver”.

You will then navigate to the Drivers Directory on the CD that came with the Hantek 365B digital multimeter and select “HANTEK DMM DRIVER”.

If the drivers were correctly installed, the Hantek 365B unit will now show up in the DEVICE MANAGER as HANTEK DMM rather than as ST MICRO.

DIY Series: Wireless Stepper Motor Control

Interested in learning more about stepper motor control? Check out our instructional video, schematics, and Arduino code below to build your very own wireless stepper motor controller — a great addition to all of your DIY home automation projects!


List of materials:

http://www.circuitspecialists.com/arduino-uno-r3-plus.html – 1 piece

http://www.circuitspecialists.com/wb-104-3+j.html – 1 pc.

http://www.circuitspecialists.com/l934hd.html – 2 pc.

http://www.circuitspecialists.com/r18-29a-black.html – 1 pc.

http://www.circuitspecialists.com/r18-29a-red.html – 1 pc.

http://www.circuitspecialists.com/uln2003a.html – 1 pc.

http://www.circuitspecialists.com/rxd4140-434.html – 1 pc.

http://www.circuitspecialists.com/nema_16_step_motor_39byg101.html – 1 pc.

http://www.circuitspecialists.com/gfp151u-5volt.html – 1 pc.

http://www.circuitspecialists.com/ra1.0k.html – 2 pc.

http://www.circuitspecialists.com/ra10k.html – 2 pc.

http://www.circuitspecialists.com/cd4013.html – 2 pc.

http://www.circuitspecialists.com/31va401.html – 1 pc.

http://www.circuitspecialists.com/2n3904.html – 2 pc.

Total Cost: $85.00 + shipping

Stepper motor control with OSEPP UNO R3 Plus and ULN2003 in FritzingImg2


RXD4140 circuit for wireless control – only channels 1 and 2 (D3, D2) are used. D1 and D0 do not need connections.



#include <Stepper.h>

int forward = 2;

int reverse = 3;

Stepper motor(200, 10,11,12,13);

void setup() {





void loop() {

int Speed = analogRead(A0);

int RPM = map(Speed, 0, 1023, 0, 100);

int f = digitalRead(forward);

int r = digitalRead(reverse);

if(f == 1 && r == 0 && RPM > 1){





if(r == 1 && f== 0 && RPM > 1){








The Best Soldering Station for Lead-Free Solder Review

There are several established brands — including Weller, Metcal, Pace, Circuit Specialists, Goot, SolderWerks (BlackJack), and Hakko — that offer quality lead-free soldering stations. Whether you work in a repair shop, research and design, or are a hobbyist, with normal use you should get several years of reliable service from a soldering station from any of these brands. You may need to replace consumables such as the soldering iron tip, heating element, and perhaps even the soldering iron handle at some point, but the main body of the soldering station should perform well for several years.

When you are selecting the best soldering station, you will want to consider what sorts of projects you’ll be working on. For instance, these days you’ll need to use lead-free solder on multi-layer boards, and you will need a soldering station with a fast temperature recovery time to use lead-free solder. If you attempt to use lead-free solder with an older soldering station that has a slower recovery time, you will be forced to increase the temperature to compensate for the slow thermal recovery time. Although this will melt the lead-free solder, the temperature will drop and not recover quickly enough, causing the solder to stop flowing. When this happens you end up applying heat for too long, which can damage parts as well as the PCB.

There are two basic methods for achieving fast thermal recovery when using lead-free solder. One is simply to design the soldering station with a higher-wattage heating element. In the past stations were often rated at about 35 to 40 watts, but today a reasonably priced soldering station will typically have a minimum of 60 watts —though it’s even better to opt for a station with a 75 watt heating element. Another popular method for improving thermal recovery is to integrate the heating element and the soldering iron tip. This method keeps the temperature at the tip very stable, as the element can react very quickly and transfer the energy to the tip almost instantaneously. The only downside to this design is that tips are quite a bit more expensive, since you are purchasing an integrated tip/heating element assembly.

Even if you do not plan to use lead-free solder, remember that Europe now requires that nearly all pieces of electronic equipment must meet RoHS environmental standards. The USA has not yet implemented this requirement, but most manufacturers of electronics products are located in Asia and they manufacture their equipment with European standards in mind. You will most likely need to use lead-free solder at some point, even in the USA, so it’s wise to pick a soldering station that can do the job when lead-free solder is necessary.

Simply smart circuitry since 1971.