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# Open-hardware for electrostatic discharge testing (O-ESD)
O-ESD is open-hardware project for (pre-compliance) [ESD immunity testing](https://en.wikipedia.org/wiki/IEC_61000-4-2) in accordance with [IEC/EN 61000-4-2](https://webstore.iec.ch/en/publication/68954) standard. It is a stand-alone battery-powered portable device that can produce low-energy voltage pulses in the range from –15kV to 15kV. All electronic devices must be immune to a certain level of ESD, as ESD happens everyday between humans and electronic devices.
![Prototype](img_O-ESD_prototype_top_view.png)<br>
<br>O-ESD is released under [CERN Open Hardware License Version 2 – Strongly Reciprocal](https://o-esd.etf.bg.ac.rs/IMG/cern_ohl_s_v2.txt).<br>
The current release is [version 1.0](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v1.0).<br>
Electrostatic discharge can irreparably damage electronic devices. Use O-ESD with caution!<br>
## Features
* Contact discharge mode and air discharge mode.
* Both positive and negative polarity of the output voltages for all levels.
* Open-circuit output voltage at terminals from 1kV to 12kV for the contact discharge.
* Open-circuit output voltage at terminals from 1kV to 15kV for the air discharge.
* Single-discharge mode and user-defined pulse repetition.
* User-defined hold time for output voltage for air discharge.
* Equivalent capacitance seen from the output terminals 100pF.
* Equivalent resistance seen from the output terminals 330&Omega;.
* ESD pulse in accordance with IEC/EN 61000-4-2.
* ESD pulse energy up to 17mJ.
* Powered by two 18650 3.7V Li-Ion rechargeable batteries.
* 15 hours of continuous operation (using fully charged 3200mAh batteries).
## Quick-Start Guide
The O-ESD is powered up (or down) using the toggle switch located on the grip. The O-ESD user interface consists of: toggle switch (ON/OFF), fire button, USB battery chargers (optional), LCD, down button, up button, multi-purpose knob located on the left side of the LCD.<br>
![Grip](img_grip.png)<br>
Once the O-ESD is powered-up the splash screen should appear for 1 s at the LCD. Afterwards, the main screen of the O-ESD shows up. LCD has four 20-character lines. Each line stands for one item. Items (i.e., lines) are selected by moving the selector “ > ” using up/down buttons.<br>
If an item has a numeric value selectable by the user, the numeric value can be changed by rotating the knob. Some items have multiple choices (selections) or submenus (sub-items) available and those are accessible by pressing the knob.<br>
![UI](img_UI.png)<br><br>
There are two modes of operation<br>
(A) contact discharge<br>
(B) air discharge.<br>
<br>The default mode is the contact discharge. The sharp conductive tip (electrode) is used for contact discharge and should be placed in the red socket at O-ESD output. For air discharge the rounded conductive tip (electrode) is used and it should be placed in the black socket. O-ESD is intended for use with only one conductive tip (electrode) inserted at a time and with the appropriate mode of operation selected.<br>
<br>Screen (menu) has four items.<br>
(1) The first (top) item on LCD is the battery status. It displays the minimum of relative voltages of the two batteries. If the voltage of a battery drops below 3.5 V, the battery status displays that recharge is needed. Note that O-ESD will work even with very low battery voltage that may irreparably damage the batteries. Battery status has a submenu that presents extended information about each battery.<br>
![Battery_extended](img_bat_ex.png)<br>
(2) The second item is the operation mode. It can be either contact or air as selected by the used.<br><br>
(3) The third item is the ESD voltage level. The ESD voltage can be in the range from –12kV to 12kV in the case of contact discharge, or in the range from –15kV to 15kV in the case of air discharge. Note that the sign of the charge (polarity) is defined by the position of the cascade, i.e., it should be placed in the correct position in order that given polarity can be produced at the output.<br><br>
(4) The forth item (at the bottom of LCD) is
* the total number of pulses in the case of the contact discharge or
* the hold time in seconds for air discharge (i.e., the time window in which the rounded tip is at the predefined voltage until the air discharge happens).<br>
Once the user has selected the mode of operation, ESD voltage level and number of pulses (or hold time), the discharge is initiated by pressing the fire button on the grip. During all the specified discharge(s) cycles, the information about discharge is displayed on LCD and the O-ESD main screen is inaccessible.<br><br>
The sign (polarity) of the output is determined by the cascade connections to the shaper and the motherboard. The opposite sign is achieved by rotating the cascade for 180 degrees, i.e., the sign of the output is the one printed on the cascade end connected to the shaper. Before disconnecting and rotating the cascade, wait for 10 seconds after the last discharge so that the cascade discharges fully.<br>
![Cascade_rotation](img_cascade_rot.png)<br>
When not in use, O-ESD should be turned off using the toggle switch on the grip.<br>
## Assembly
O-ESD consists of six parts:<br>
(1) Mechanical support.<br>
(2) Grip.<br>
(3) Cascade.<br>
(4) Shaper.<br>
(5) Claws and strap.<br>
(6) Motherboard.<br>
Bill of materials (BOM) is available at link.<br>
Design files are available at link.<br>
![Mechanical_parts_front](img_mechanical_parts_front.png)<br><br>
![Mechanical_parts_back](img_mechanical_parts_back.png)<br><br>
![Mechanical_front](img_mechanical_front.png)<br><br>
![Mechanical_back](img_mechanical_back.png)<br><br>
### Mechanical support
Mechanical support consists of laser-cut acrylic glass, bolts, nuts and spacers, all made from nonconductive materials.<br>
![Mechanical_parts](img_mechanical_parts.png)<br>
### Grip
The grip is a separate PCB connected to the motherboard with 4-wire cable. The main purposes of the grip are: to house batteries, to provide physical grip of O-ESD and to house toggle switch and fire button.<br>
![Grip_assembly](img_grip_assembly.png)<br>
### Cascade
The cascade is a separate PCB connected to the motherboard and the cascade with two 2-wire cables with XT60 connectors at each end. The main purpose of the cascade is to provide high-voltage DC for the shaper.<br>
![Cascade_assembly](img_cascade_assembly.png)<br>
In order to prevent losses from the corona effect, assembled cascade can be coated with corona-protective insulating material (e.g. Plastik70 from Kontakt Chemie or similar).<br>
### Shaper
The shaper is a separate PCB connected to the mother board (with 4-wire cable) and the cascade (with 2-wire cable with XT60 connector). The main purpose of the shaper is to generate pulse according to IEC/EN 61000-4-2.<br>
![Shaper_assembly](img_shaper_assembly.png)<br>
In order to prevent losses from the corona effect, all conductive surfaces on the top layer of the assembled cascade (except the flat-cable connector) can be coated with corona-protective insulating material (e.g. Plastik70 from Kontakt Chemie or similar).<br>
### Claws and strap
The strap is 2 m 34-wire flat cable connected to the cascade with 34-bin boxer connector. The other end of the strap is connected via 34-pin boxer connector to PCB with claws for GND contact. The main purpose of the claws is to provide easy way of connecting the ground of O-ESD, while the strap connects the O-ESD and the claws.<br>
![Claws_assembly](img_claws_assembly.png)<br>
### Motherboard
Motherboard is a separate PCB connected to the grip (with 4-wire cable), to the cascade (with 2-wire cable with XT60 connector) and to the shaper (with 4-wire cable). The main purpose of the motherboard is to orchestrate the functioning of O-ESD and to provide the user interface. <br>
![Motherboard_assembly](img_motherboard_assembly.png)<br>
All components of the motherboard except step-up transformer are available on the market. The step-up transformer must be assembled per specifications.<br>
![Trafo_assembly](img_trafo_assembly.png)<br>
The transformer has the following roles<br>
(a) to accumulate energy while the switching transistor is in the on state and release that energy to the high-voltage cascade when the switching transistor goes to the off state<br>
(b) to provide step-up voltage transformation from the low-voltage input to the high-voltage cascade and<br>
(c) to provide galvanic insulation between the low-voltage input and the high-voltage cascade.<br>
<br>Windings:<br>
(1) The primary and the secondary are to be wound on the coil former.<br>
(2) The total number of turns for the primary winding is 4.<br>
(3) The total number of turns for the secondary winding is 1860, i.e., about 155 per layer, 12 layer in total.<br>
(4) The sense (direction) of the windings should be the same.<br>
(5) The high voltage (secondary) winding shall be wound first. The low voltage (primary) winding shall be wound on top of it.<br>
![Trafo_ends](img_trafo_ends.png)<br><br>
Winding can be performed using a winding machine or produced manually, with care. The number of turns per layer of the secondary winding can be counted or can be estimated from the inside length of the coil former and the wire AWG.<br>
Regardless of the winding method, the beginning of the high voltage coil, which comes closest to the ferrite core, shall be inserted in heat shrink tubing and the tubing shall be heated to its final dimensions. The tubing is used to improve the insulation between the wire at the beginning of the coil and other wire layers.<br>
<br>Once a winding layer is completed, it shall be fully covered by layers of insulation paper. The total thickness of the insulating layer must be at least 0.2 mm. The first role of this insulation is to reduce the parasitic capacitances between adjacent wire layers. The second role is to increase the breakdown voltage between adjacent wire layers.<br>
The completed secondary winding shall be covered by layers of insulation paper either fully or only in the area where the primary winding is going to be placed. The main role of this insulation is to increase the breakdown voltage between the two windings.<br>
<br>Once both windings are completed, the insulation from all wire ends shall be removed. Solder the terminals of the primary and secondary windings according to raster view. The beginning of the secondary winding (which is covered by the heat shrink tubing) shall be soldered to the pin denoted by the red circle in raster view.<br>
Insert the two halves of the ferrite core into the coil former shown in assembly of the step-up transformer. The cross sections of the core in the areas denoted by green ellipses should have gaps of 0.25mm to 0.3mm. Cut three pieces of the standard printing paper (80 GSM) paper per gap, and stack pieces to form the gap. It is not necessary to place the paper in the central column of the core.<br>
![Trafo_core_clips](img_trafo_core_clips.png)<br><br>
Secure the transformer by two clips. One clip is shown in Sketch of a clip. The location of the clips can be seen in assembled step-up transformer.<br>
## Use-case scenarios for testing and demonstration
Five use-case scenarios for electrostatic-discharge testing and demonstration of ESD effects are [presented](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Demos#).<br>
Assembly instructions and explanations, including videos, can be found on [O-ESD GIT](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Demos/Readme_demos.pdf).<br>
## Development
This part contains development milestones with accompanying documents.
### 1. Technical requirements
The technical requirements for O-ESD hardware are summarized along with a review of multiple ESD guns available on the market. Technical specifications of hardware on the market are compared to the specifications from IEC61000-4-2 standard.<br>
[Technical requirements](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/raw/branch/main/Documents/O-ESD-01.pdf)
### 2. Schematics and considered realizations of high-voltage generator for O-ESD
Various approaches considered as possible solutions for O-ESD are given along with the schematics in LTspice program. <br>
[Schematics and possible realizations of high-voltage generator for O-ESD](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/raw/branch/main/Documents/O-ESD-02.pdf)
### 3. Trade-offs and cost-benefit analysis of considered solutions
The cost-benefit analysis of considered solutions is done by taking into account the availability of electronic components on website of online distributors of electronic components. The understood trade-offs for considered solutions are given.<br>
[Trade-offs and cost-benefit analysis of considered solutions](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/raw/branch/main/Documents/O-ESD-03.pdf)
### 4. Design and prototype printed-circuit boards for all candidate solutions
All considered solutions are prototyped. Since some candidate solutions share some components or parts, PCBs/prototypes are made for functional parts that can be mixed and matched between O-ESD solutions. For all considered parts that have PCB, Gerber and drill files (needed for the production) are given. The photos of prototypes, functional parts and considered components are provided, too.<br>
[Snapshot of current hardware development](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development)
### 5. Prototype assembly (v0.1) and microcontroller software
Three prototypes are assembled (v0.1). [Prototype photos](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development/Prototypes).<br>
Microcontrollers are tested on ESD. [Report, photos and codes for ESD testing of microcontrollers](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development/3-Controllers/ESD_testing).<br>
Software for microcontrollers for the user interface is written. [Software for user-interface](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Software_development).<br>
Based on testing results: new double cascade is designed in KiCAD, PCB for flyback and push-pull is designed in KiCAD, new trafos are designed and assembled and DC/DC converters and battery chargers in the power supply are considered.<br>
### 6. Performance assessments and prototypes v0.2
Assessments of technical performances of O-ESD prototypes v0.1 are done and results can be found in [Assessment results v0.1](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development/Measurements/v01).<br>
In accordance with measurement results the shapers are redesigned. [Redesigned shapers](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development/5-Shapers)<br>
[Design decisions](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/Hardware_development/Measurements/v01/Design_decisions.txt) are made for the O-ESD.<br>
### 7. O-ESD prototype v0.5 assembly and verification
Bill of materials (BOM) for O-ESD v0.5 can be found at [BOM v0.5](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/Bill_of_materials.txt)<br>
Drawings, schematics, production files and photos of assembled parts can be found at [1-Hardware](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/1-hardware) in separate subfolders.<br>
[A sketch of O-ESD v0.5](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/O-ESD_v0.5_drawing.jpg) and a photo of [O-ESD v0.5 assembled prototype](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/O-ESD_v0.5_assembled.jpg) are presented.<br>
[Software for O-ESD v0.5](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/2-software) is available as well.<br>
Finally, the [measurements](https://o-esd.etf.bg.ac.rs/forgejo/dragan.olcan/O-ESD/src/branch/main/v0.5/3-measurements) confirm that O-ESD v0.5 can produce standardized ESD current pulses for all contact discharge levels (2kV, 4kV, 6kV and 8kV, both positive and negative pulse voltage), as well as air discharge up to 15kV (both positive and negative).<br>
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