Open-Source Leg

E-Stop Setup and Use

The E-Stop (Figure 1) is a handheld emergency stop switch developed by the Neurobionics Lab. It can be used for high current/high power DC powered devices, and therefore, is well suited for use with devices such as the OSL. The E-Stop consists of a PCB connected to a handheld switch. To use the E-Stop, connect it in series between the device’s DC power source and the powered actuator. This page provides a step-by-step guide on how to order parts, how to assemble the E-Stop, and how to use it.

Figure 1: Custom E-Stop PCB with PCB case underneath

Table of contents

1. Overview
2. Ordering components
3. Assembly
4. Use
5. All files

1. Overview

The E-Stop does not need a dedicated power source as it is designed to share the same DC power source as the DC device it is connected to, therefore, when selecting components used for the E-Stop, the design attempted to minimize the following criteria:

  1. Footprint- by using SMT components
  2. Power consumption- by MOSFET selection
  3. Number of vendors that stock parts need to be purchased from

The vendors employed along with the cost associated with each vendor are enumerated below.

  • Mouser (PCB components) ~$29.44
  • OSH Park (PCB) ~$2.22
  • Amazon (connectors) ~$9.05
  • Shapeways (3D printed parts) ~$51.08
  • Total Cost ~$91.79

The E-Stop’s specifications are given in the table below:

E-Stop DC Power Source Specifications
ParameterRange
DC Power Source Voltage11 V – 50 V
Current0 A – 15 A
2. Ordering components

The components required for the E-Stop can be separated into three categories: manufactured, prefabricated, and miscellaneous. All of these components can be found in the E-Stop Bill of Materials. Due to recent supply chain issues, the MOSFET required has occasionally been out of stock. A suitable replacement that can be ordered internationally can be found here.

  1. Manufactured components
    • PCB
      In order to order the PCB, this ZIP folder containing the necessary Gerber files need to be uploaded to OSH Park’s website. Please make sure that the option for “2 oz copper, 0.8 mm thickness” is chosen.
    • 3D printed parts
      In order to order the 3D printed parts, these STP files need to be downloaded and uploaded to Shapeway’s website. I highly recommend versatile plastic as the printing material. Printed using selective laser sintering (SLS), versatile plastic is a durable nylon plastic.
  2. Prefabricated components
    Please refer to the E-Stop Bill of Materials on which prefabricated components to purchase. These prefabricated components consist of SMDs for the PCB and connector components (e.g. the cable that connects the switch to the board, bullet connectors, etc.).
  3. Miscellaneous components
    Please refer to the E-Stop Bill of Materials.
3. Assembly

Use the following steps to assemble the E-Stop. Although the end user may use any connector type, this assembly procedure uses 3.5 mm bullets for connectors between the board and DC power source and between the board and powered actuator.

Using solder paste and the hot air rework station

Attach every SMD (Figure 2) using solder paste and a hot air rework station. 340 °C worked well for me (do not expose board to hot air for too long or you risk damaging SMT components).

Figure 2: Populated front and back sides of PCB

Using a soldering iron

  1. To connect 3.5 mm bullets to battery and system 16 AWG wires, melt solder into bullet’s orifice where wire goes and insert wire before solder solidifies.
  2. Solder 16 AWG wires to board to pads on underside of board in order to keep top side of board looking neat.
  3. 4 Pole Aux Cable
    • Cut into aux cable and you will see four conductors inside (Figure 3):
      1. Ground sheath composed of stranded wires (may be combined already)- connected to base pole on the male connector end
      2. Black insulated wire- connected to pole next to base pole on male connector end
      3. White insulated wire- connected to pole next to top pole on male connector end
      4. Red insulated wire- connected to top pole on the male connector end
    • For each side of the aux cable, combine ground sheath strands into one insulated wire by using shrink wrap as seen in Figure 3 (ground sheath may already come braided together).
    • Using the female connector side of the aux cable, solder the four conductors to the Switch and D1 through holes:
      1. White wire goes into one of the two Switch through holes.
      2. Black wire goes into the other Switch through hole.
      3. Ground sheath goes into the positive D1 through hole.
      4. Red wire goes into the other D1 through hole.
    • Using the male connector side of the aux cable, solder the four conductors to the DPDT switch’s pins (using pins 1 and 2 on one side and the diode pins):
      1. Ground sheath goes to positive diode pin (one without red dot) and red wire goes to negative diode pin.
      2. White wire and black wires go to pins 1 and 2, order does not matter.
      3. Shrink wrap the DPDT switch appropriately as seen in Figure 4.
Figure 3: a) Aux cable with section of braid removed and outer insulation stripped b) Ground sheath separated from white, black, and red conductors c) Ground sheath strands combined with heat shrink and white, black, and red conductors stripped
Figure 4: Shrink wrapped DPDT switch

Using a hot glue gun

  1. Strain relief battery leads, motor leads, and switch leads with hot glue (Figure 1). Make sure to cover the terminals pads to decrease likelihood of short. I’d also suggest covering the terminals on the underside of the board also.
  2. To make hot glue look neat, it is suggested to place hot glue on board using hot glue gun and then use a hot air gun to smooth the hot glue (do not expose board to hot air for too long or you risk damaging SMT components).
4. Use

Attach actuator leads to appropriate MMI terminals on the board. Then attach ground BM1 wire to DC power source. Then finally attach Positive BM1 leads to batteries. Figure 4 shows the E-Stop connected to a generic DC powered device as an example.

Figure 4: Connecting the E-Stop between a power source and a powered actuator for a generic DC powered device

After everything is connected, to cut power to the actuator, simply depress the switch button. The aux cable is wired so that in the scenario where the DPDT switch is not connected to the board, this scenario is equivalent to when the DPDT switch IS connected to the board and the switch depressed (i.e. disconnecting the DPDT switch without depressing the bottom will also cut power to the system). This serves as an alternative method of disconnecting power to the system in the situation where pressing the button is not feasible. The DPDT switch is placed inside a handle for comfort and to prevent damage to the switch soldering (Figure 5).

Figure 5: Board (shown inside its case) connected via aux cable to switch (shown inside its handle)

There is no danger associated with only inserting the male connector of the aux partially into the female connector. The only downside is that if the male connector is inserted 75% of the way, the 86.6 kOhm resistor (R1) is subjected to a larger voltage; however, this additional voltage does not lead to the resistor exceeding its power rating.

5. All files

All of the files needed to make the E-Stop and additional files can be found here for your convenience. The additional files include circuit schematics, Diptrace files used to create the board CAD, etc. A report on the E-Stop is also included for those who want details on how the E-Stop was designed along with detailed performance specs.