Modified USB Isolator
David Peters shared his modifications to my USB Isolator board. The board can be seen on a title picture (click on it to make it bigger), the design files can be downloaded and below is the list of modifications:
- Isolated VBUS supply has been added
- DC/DC converter can be enabled or disabled by jumper to choose external power supply
- 7805 linear regulator can be used instead of DC-DC converter
- Optional additional capacitors for better filtering
- Enumeration reset possible with jumper
- LEDs for input and output power visualization
- Isolation between areas is 6mm providing ~600V protection
Linear power supply
Several days ago I received an e-mail from Larry Owens, my fellow Coloradoan. Larry is Hi-Fi enthusiast; he built USB isolator kit and made very elegant and clever modification to it – a linear power supply. Larry’s design fits on existing board footprint.
Here is a quote from Larry’s e-mail:
Thought you might like to see what a little creativity can yield — did not fancy a SMPS’s noise, but wanted to be able to handle various battery sources. Since the off-board supply would be rather quiet, just selected a plain old 7805C (found in drawer, able to dissipate plenty of heat w/ 12v+ supplies and full 500mA USB loads). Thought a power-up LED would be nice too… …the challenge was to find existing pads for all components without having to use any cut/jumps… do consider that outcome lucky at the least…
Take a look at the title picture (click on it to make it bigger). TO-220 next to the barrel connector is old trusty 7805 linear regulator. Small bypass capacitor is soldered between output and ground pins of it. Input and output pads are occupied with electrolytic caps, 100 ohm ( @100 MHz ) ferrite bead sits on inductor pads. Finally, a small LED is mounted in place of 3300pF cap with current-limiting resistor across LT1376 pins 7 and 8.
This is it – simple, elegant and very useful. Thanks again, Larry for sharing the design and very nice and clear picture!
Long overdue USB Isolator Assembly Guide
is finished. It describes building Analog Devices ADuM4160-based USB Isolator kits
. The guide contains component identification, step-by-step building instructions and soldering hints. Those who has their isolators already built will find useful powering and tweaking information at the end of the guide.
If you see any errors or have any questions, please let me know!
A reel of ADuM4160s
I’m pleased to announce that the long wait is finally over – I’m now in possession of a reel (this is 1000 pcs!) of ADuM4160 – the core chip of USB Isolator
. I will be shipping back orders today and tomorrow – if you have ordered any of USB Isolator products from me in February, March, or April, and will not have gotten shipping notification by Monday, please contact me.
USB Isolators are back in stock. By popular demand, I also started selling ADuM4160 in single quantities – look in components section of the store.
On a side note, I received an e-mail from a company in Denmark offering ADuM4160-based USB Isolators in “complete” form – sporting a nice looking case and bus-powered supply for the peripheral side. I bought one yesterday to take a look. I’m going to write a review and, if I like it, start reselling it.
ADuM4160 PIN pin grounding
Q. I am getting “USB device not recognized” error message – what do I do? Also, since the isolator is soldered into my circuit, “reconnect peripheral” suggestion seems too difficult to follow.
I decided to write this article after receiving several e-mails from people who bought my isolator. While setups described in those e-mails were different, the problem was the same – a PC refusing to recognize the device connected through the isolator. Here I will try to explain what is happening and also share my ideas how to troubleshoot and possibly fix the problem.
When nothing is connected to USB port, the bus is held at ground level with pull down resistors on the host side. USB device, when connected, pulls one of bus lines up, often times also with a resistor connected to Vbus and data line. Host sees it, sends bus reset and tries to query the device. If device is answering, host keeps querying the device and eventually enumerates it. When device is enumerated, application takes over.
If device is not answering (like for example, when self-powered device is turned off), host will give up and post “Device not recognized” message. To get attention from the host, we need to generate bus event, i.e., disconnect the peripheral and connect it back again.
Continue reading USB Isolator Most Frequently Asked Question
USB Isolator Board Solder Stencil
I received a batch of solder paste stencils for my USB Isolator PCB. Now those who want to try low-tech reflow soldering technique, can do it. Stencils are laser cut by Ohararp from 0.0035″ Kapton. They are now offered for sale at the store.
USB Isolator parts
Immediately after announcing USB Isolator circuit I received several suggestions to put together a parts kit. Indeed, users of such devices are usually not afraid of small parts and generally aware of which side of soldering iron is better suited for holding on to. Also, I’m having hard time trying to find a supplier, where one can buy all the parts to build this circuit; usually, you need to buy from 2-3 suppliers, which significantly adds to shipping expenses. Considering this, I’m now offering not one, but two parts kits to build an USB Isolator based on Analog Devices’ ADuM4160.
The kits are added to “ADuM4160 USB Isolator bare PCB and kits” dropdown. One kit contains all the parts necessary to build an isolator – PCB, ADum4160, capacitors, resistors, USB connectors, pin headers, and jumpers and costs $25. Another kits contains all that plus all parts for 5V buck converter – LT1376-5, inductor, caps, etc and costs $33. Enjoy!
I’m not writing a build manual at this time; I’d like to get some feedback from builders first. Any questions you have, please don’t hesitate to ask.
ADuM4160 USB Isolator PCB panel
USB Isolator PCBs has arrived. In this article I will be talking about building and configuring one. The PCB was designed with hobbyist-friendly large size SMD packages and 10mil clearances and I hope it won’t be difficult to made one at home. The layout files are available from downloads section.
Let’s talk about parts procurement. This is a BOM at Mouser sans ADuM4160, LT1376-5, and PCB. This is BOM at Digi-Key, which includes LT1376-5. Last time I checked, Digi-Key was way more expensive. As far as ADuM4160, since no one sells it in single quantities right now (check this using FindChips), the easiest way to get it is to ask Analog Devices for a sample, they are generous folks.
Continue reading Building USB Isolator.
[ Update ] I now have bare PCBs and parts kits of this design for sale in store, as well as assembled and tested boards.
We all love USB. It is well supported across many platforms, easy to work with, and even able to provide a little power to the peripheral. However, the quirk of USB is that peripheral must share ground line with the host. The host is usually a PC and very often a desktop, which means it’s USB ground is electrically connected to earth ground in the wall outlet. With PC-based test instruments, like oscilloscopes, logic analyzers and such, It works fine most of the time, but not always.
There are situations when we prefer our ground separate. It happens when PC/earth ground is too “dirty” and we don’t want our circuit to pick up this dirt. Sometimes our device’s ground is not too good or even dangerous if connected to earth ground. Sometimes we are trying to overcome ground loops. Sometimes, we want our oscilloscope to behave like a multimeter, i.e. being able to show voltage drop between any two arbitrary points of the circuit. In any of this cases we want our USB data and ground isolated from the host.
Isolation improves common-mode voltage, enhances noise rejection, and permits two circuits to operate at different voltage levels. It also tends to save test equipment, as well as PC itself. It is also very useful in industrial setting, that probably why industrial USB isolator devices cost between $200 and $400. While looking for a solution for my lab, I found interesting USB isolator part, recently released by Analog Devices, and decided to give it a try.
Continue reading USB Isolator.