While designing USB Isolator I needed a 5V supply to power the device side. I picked Linear Technology LT1376-5 part which proved to be pretty reliable and mellow converter. I’ve had used this part for 3.5 years now, in a product and also in the kit and I haven’t had any serious issues with it. Some time ago I decided to put together another kit based on the same controller – at this time containing only PTH components to make assembly easier for beginners. This kit is now available at the store for $20 plus shipping and the following is a short overview of the capabilities.
The kit contains a PCB plus all parts necessary to build a DC-DC step-down converter. Voltage setting resistors to make output of 3.3V, 5V and 12V are included. The converter is capable of supplying 1A at any of the output voltages over 6-25V input voltage range ( 23Vmax for 12Vout), and can be pushed up to 1.3A if input and output voltages are close enough. Output voltage ripple is 50mv@1A.
The biggest advantage of switch mode supplies is efficiency. It is possible, for example, to step down from 24V to 3.3V without generating excessive heat even at 1A load. Also, switchers are fascinating circuits, fun to build and play with.
In addition to full kit, a bare PCB is offered for makers who prefer to source parts themselves. Eagle CAD files of the circuit are also available.
120ma Inductorless DC-DC converter
Today’s electronic projects often require more than one supply voltage. 5V is often used to power MCUs, while sensors and peripheral interface controllers usually need 3.3V – if both types are used in your circuit, both voltages must be provided. Typically, one of the voltages is produced from the main supply (battery, wall wart, etc.) and the second voltage is then derived from the first using either linear LDO regulator if the second voltage is lower than the first or a boost converter if the second voltage is higher.
The boost converter I’ve designed uses Microchip MCP1253 charge pump controller. It doesn’t use an inductor and is capable of providing selectable 5V or 3.3V output voltage and up to 120ma of output current. The converter is half-inch long and weighs just 0.5g. All through-hole pads are placed on 0.1″ grid making it breadboard-friendly. Thanks to inductorless desgn, the converter is inexpensive, stable, and easy to use while providing automatic switching between step-down and step-up modes, and offering extra options, such as external shutdown and supply monitoring. The following picture shows board connections (click on it to make it bigger):
- Vin, Vout, GND are the only connections necessary out of the box (they are marked on the other side of the PCB). Input voltage can be 2.0-6.0V, output voltage is set to 5V. The converter automatically switches from buck to boost, therefore it is possible, for example, to have regulated 5V output in the whole discharge range of a battery of four alkaline cells (3.6-6V), or 3.3V from a single LiPo (if you switch output voltage to 3.3V, see below). The output current is 120ma, maintained down to 2.8 Vin at 5V Vout
- 3-pad Vout set jumper is set to 5V by a shorting middle pad to the right one. To switch output voltage to 3.3V remove the short using solder wick and short middle pad to the left one
- Shutdown The converter can be stopped by pulling this signal low. By default, it is hardwired to Vin, in order to use it, you need to cut a trace inside Shutdown enable jumper. The jumper can be later closed, if necessary, similarly to output voltage selector
- Power Good This signal falls low when output is out of regulation, which can indicate low battery or excessive load. In order to use this signal, a 100K 0603 resistor must be soldered on vacant pads indicated by the arrow Power Good Resistor
Design files are available for download. Fully populated and tested boards are offered for sale at the store. If there is enough interest, I can also offer blank PCBs as well as boards preconfigured for 3.3V output voltage. Please leave a comment if you’d like these options added.
USB Host 2.0 connected to Arduino Mega 2560
A major revision of USB Host Shield for Arduino has been released and is available in the store. The board’s improved layout makes this shield compatible with more Arduinos, makes it easier to use and opens new possibilities. The main differences from rev.1xx are outlined below:
- The SPI interface has been moved to ICSP header making shield compatible out of the box with “big” Arduinos – Mega and 2560. Standard size boards, such as Duemilanove, UNO, as well as clones with classic connector layout, are also compatible with this revision of the shield. This compatibility is maintained on a software level as well – all necessary code changes are performed using conditional compilation preprocessor directives.
- USB connector has been moved to the opposite side of the board. All external connectors are now in the same place making enclosure layout easier.
- MAX3421E RESET line is no longer handled by dedicated Arduino pin. While MAX_RESET pin is still used in current version of USB Host library, it will be dropped from the next major revision of the code.
USB Host Shield 2.0 with AVR Dragon
Besides “Mega-formfactor” compatibility, connecting to Arduino SPI signals on ICSP connector has several advantages. First of all, in this layout traces are much shorter and as a result, the shield works more reliably at higher SPI speeds and/or larger signal and power noise. Second, since the 2X3 connector, which comes bundled with the shield, is of ‘stackable’ variety, it is possible to connect AVR Dragon or other ICSP programmer to Arduino while USB Host Shield is mounted – picture on the left shows the arrangement. Finally, pins 11-13, occupied by SPI signals on “classic” Arduinos, are vacant on Megas and also uncommitted on the shield. Therefore, they can be used for other purposes without USB library code modifications.
The shield comes in 2 configurations. One, called “Standard” is compatible with official full-size Arduino boards (Duemilanove, UNO, Mega, Mega 2560, and possibly others), as well as clones which supply both 3.3V and 5V to the shield. One example of such clone is BlackWidow; if you are aware about other compatible clones, please let me know.
Another configuration, called “3.3V” is designed for battery-operated projects. It is compatible with Sparkfun’s Arduino Pro 3.3V board (I’m not aware of any other 3.3V-only full-size clones). It also supplies 3.3V to VBUS instead of spec’d 5V, therefore some bus-powered devices may function erratically (but not necessarily; I actually use bus-powered USB flash drive during final testing of production 3.3V shields). Self-powered devices, such as digital cameras, usually don’t care about VBUS voltage at all. Additionally, board layout makes it possible to mount external power supplies to generate 5V from 3.3V and vice versa, if necessary.
The shield is compatible with current version of USB library. It is also very similar to rev.1.xx shield and information from previously posted articles is mostly valid for 2.0 board. Schematic and Eagle CAD files are also available for download. I am currently working on detailed description of the shield and hoping to get it ready in a week or two.
Along with this shield I will continue producing rev.1.21 board – there are still “not-so-compatible” Arduino clones around. However, next major revision of USB library will not be compatible with rev.1xx shields; it will be possible to make it work after minor hardware/software modifications.
As always, your questions and comments about the product are welcome and appreciated.
USB Host mini in test fixture
The first batch of USB Host Minis is built, tested, and boards are available in store. It is designed to be employed in lightweight, battery-operated circuits, for example, used for digital camera control. It can also be used as general MAX3421E breakout board. Title picture shows the board proudly sitting in its’ own ghetto-style Sparkfun-inspired pogo bed.
The design follows Arduino Mini minimalistic approach. It is 3.3V only and mates quite nicely with Sparkfun 3.3V Arduino Pro Mini. Only essential control and GPIO signals are available – no power supplies, level converters, or even jumpers are provided due to lack of space. However, since rearranging control signals is often necessary, extra pads have been placed for this purpose. They can be seen on product picture at the top and to the left of MAX3421E IC.
The board has VBUS routed to 3.3V. Even though the voltage is lower than specified 5V, the shield has been tested to work flawlessly with numerous self-powered devices, such as digital cameras, as well as some bus-powered devices, such as Sandisk Cruzer flash drive. However, if 5V VBUS is necessary, board can be easily modified – the trace from 3.3V to VBUS can be cut and 5V applied using a pad placed on the board for this purpose. It can be arranged using single 5V supply; since Arduino Pro Mini has on-board LDO, 5V can be applied to VRAW and VBUS while shield will be getting its’ 3.3V power from Arduino board, as usual.
Bottom picture shows my favourite arrangement – Arduino Pro Mini sits on top of the shield with its’ programming connector easily accessible from either side. Also, Arduino reset switch is easily accessible this way.
Project files and schematic are available in Downloads section. If you have any questions about this design, e-mail me or leave a comment here.
USB Host Mini and Arduino Pro Mini
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.
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.
MAX3421E on a tray
I just took delivery on a batch of MAX3421Es from Maxim. They are available for sale in the store
The MAX3421E makes the vast collection of USB peripherals available to any microprocessor, ASIC, or DSP when it operates as a USB host. For point-to-point solutions, for example, a USB keyboard or mouse interfaced to an embedded system, the firmware that operates the MAX3421E can be simple since only a targeted device is supported.
This controller is supported by open source firmware that I’m developing for 8-bit microcontrollers, including PIC18s and Arduino.
MAX3421E breakout boards
First batch of MAX3421E arrived today, three days ahead of schedule, from PCBcart
. The quality is good. It’s now for sale
in my store, price $8.50.
In a week, I will be selling main Maxim parts for this board, as well as less exotic components, such as 12MHz quartz crystals and USB A connectors. If you want to get notified when it happens, send me an e-mail. In the mean time, you can try to go sample route , Maxim is known to be generous, at least to US residents.
[Update] I now have MAX3421Es for sale, price $8.00.