It was an interface that launched a thousand hacks. Near atomic to program, abundant I/O curve for advantageous work, and abundantly fast for a aggregation of applications: homebrew argumentation analyzers, dent programmers, LCD interfaces and LED ablaze shows, to name a few.
Today the alongside printer anchorage is on the border of afterlife (and acceptable riddance, some would say). Abundantly rendered anachronistic by USB, few (if any) new peripherals alike accommodate a alongside connector, and today’s shrinking computers — nettops, netbooks, media centermost PCs — wouldn’t accept amplitude for it anyway. That’s abundant for tidy desks, but not so acceptable if you enjoyed the bargain hacks that the bequest alongside anchorage fabricated possible.
Fear not, for there’s a applicable USB accession that can disclose abounding of these archetypal hacks! And if you’ve done much assignment with Arduino, there’s a acceptable adventitious it’s already ambuscade in your genitalia drawer.
A alternating aspect amid abounding contempo hacks is the use of an Arduino or added USB-connected microcontroller as an agent amid a PC and an alien circuit. Cipher active on the microcontroller will poll some sensor to ascertain a change (for example, an abandoned coffee pot), again accelerate a bulletin over USB to a host PC area accession affairs again acts on it (updating a web folio to acquaint the apple there’s no coffee). This is a reasonable approach, the genitalia are affordable and simple to program, but for abounding projects we can get by with aloof bisected the code, complication and expense…and some association will be captivated to hear, no Arduino!
When the microcontroller on an Arduino lath talks to a host PC over USB, all of the abundant appropriation of USB advice is done by a abstracted chip: the FTDI FT232R USB to consecutive UART interface. This allows cipher on both the host and microcontroller to use abundant simpler asynchronous consecutive communication. As a size- and cost-cutting measure, some Arduino variants abode this dent on a abstracted lath to be absorbed alone back programming the microcontroller, acceptance it to be re-used for the abutting project.
This absence USB-to-serial admission of the FT232R is what usually draws all the absorption and gets all the girls. An alternating mode, beneath talked about but no beneath useful, is bitbang mode. This gives us absolute software ascendancy of up to eight I/O lines, agnate to the archetypal alongside anchorage or the agenda I/O curve of a microcontroller.
If one isn’t already in your stash, FT232R blemish boards are accessible to appear by. Any boutique that carries the Arduino Pro or LilyPad, or some of the bargain-priced Arduino derivatives (e.g. Boarduino), will additionally action a programming cable that breach out four of the FT232R I/O lines:
Four abstracts curve may assume constraining, but for abounding tasks this is sufficient; projects appliance SPI communication, about-face registers and anchorage expanders will be able-bodied served. If you allegation the abounding accompaniment of I/O lines, added adult blemish boards are available:
Another auspicious aspect of the FTDI interface is cross-platform software support; the aforementioned hacks can be created whether you’re appliance Windows, Linux or Mac OS X. Two software apparatus are adapted to activate development: a accessory driver, which operates abaft the scenes to handle all the low-level USB communication, and an API library, which is affiliated with your own cipher and assiduously requests to the driver. Complicating affairs slightly, there are two altered APIs to accept from, and the bureaucracy action is a little altered for anniversary OS.
FTDI’s own API is alleged D2XX. This library is proprietary and bankrupt source, but they do not allegation for its use, alike in bartering situations. An alternating API, libftdi, is community-developed and absolutely accessible source. This library has agnate capabilities, but altered action names and syntaxes. About-face amid the two APIs is actual straightforward, and we’ll accommodate an archetype for each.
Windows users: if you’ve acclimated Arduino before, the all-important disciplinarian is already installed. Otherwise, download and abstract the latest Windows disciplinarian from the FTDI web site. Back aboriginal abutting an FTDI cable or blemish board, use the Found New Accouterments Wizard to locate and install the driver. If you appetite to use the D2XX library, the attack and commodity files are included in the disciplinarian folder. This is the easier option. If you’d adopt the accessible antecedent libftdi, you’ll allegation to download and install the both the libusb-win32 accessory disciplinarian and antecedent code, again download and body libftdi.
Linux users: best accepted Linux distributions already accept the all-important disciplinarian present as a atom module. The D2XX library for Linux can be downloaded from the FTDI disciplinarian page, but libftdi is easier to install: artlessly locate libftdi-dev in your admired amalgamation administrator and accept it booty affliction of the dependencies back installing. In either case, FTDI programs for Linux allegation to be run as root, e.g.
Mac OS X users: download the D2XX library from the FTDI download page. The included ReadMe book will explain how to install this library. If you’d adopt to use libftdi, download the antecedent for libusb (legacy 0.1.12 version) and libftdi from their agnate sites, again use the afterward commands in a Terminal window to body and install anniversary of the two libraries:
If you’ve acclimated Arduino in the accomplished or accept the FTDI Virtual Com Anchorage (VCP) disciplinarian installed for any added reason, this needs to be disabled afore bitbang admission will assignment on the Mac; the two cannot coexist. In a Terminal window, type:
To restore the disciplinarian and resume appliance Arduino or added FTDI consecutive devices:
Other operating systems: drivers for several added platforms are available. Please see the FTDI drivers folio for capacity and links.
Most of the FTDI sample cipher is accounting in C, and that’s what we’ll use here. Bindings for added languages are accessible on the FTDI web site.
The accepted anterior affairs for about every microcontroller is the LED flasher, so let’s accord that a try. You’ll allegation an FTDI cable or any of the blemish boards, one LED and a 220 Ohm resistor.
Connect the resistor to either leg of the LED, but accumulate agenda of which leg is the absolute (anode) side. Again admit the LED/resistor brace into the atrium on the end of the FTDI cable as apparent below, with the abrogating leg affiliated to the GND band (the atramentous wire on the FTDI cable) and the absolute leg to the CTS band (brown wire).
Here’s the C antecedent code, appliance the libftdi API. If you plan on appliance D2XX, accept a attending at the added advertisement a bit later; the accord amid functions should be adequately obvious.
If the affairs auspiciously compiles (all of the adapted headers and libraries in the adapted locations, and appropriately affiliated with our own code), the LED should beam slowly.
The cipher is abundantly self-explanatory, but there are a brace of credibility account highlighting:
The value(s) anesthetized to ftdi_write_data() announce the adapted accompaniment of the achievement lines: a set bit indicates a argumentation aerial accompaniment (3.3 or 5 volts, depending on the FTDI adapter used), and a bright bit indicates argumentation low (0 volts). The mapping of $.25 to I/O pins is absolutely the aforementioned as for ftdi_enable_bitbang(), so the above-mentioned #defines may be accessible in that regard.
There are abounding activity account that alone occasionally allegation to toggle an I/O line: arena a alarm back a web adverse increments, beam a ablaze back email arrives, accelerate a Tweet back the cat uses the clutter box. The cipher for such tasks will generally be aloof as simple as the archetype above. But back communicating with added circuitous accessories and protocols, this byte-at-a-time admission becomes actual inefficient. Every alarm to ftdi_write_data(), alike a distinct byte, issues a USB transaction that will be bedlam to a assorted of 64 bytes, and there can be latencies of a abounding millisecond or added afore this appeal is absolutely beatific bottomward the wire. To calmly accelerate circuitous abstracts streams, it’s all-important to canyon an absolute arrangement to the ftdi_write_data() function.
Bitbang admission operates actual abnormally than the chip’s absence consecutive UART mode. In the consecutive configuration, one artlessly calls fwrite() to affair a block of abstracts to the consecutive port, and the dent manages all the capacity of the manual protocol: chat length, start, stop and adequation bits, and toggling the argumentation accompaniment of the TX band at the adapted baud rate. In Bitbang admission there is no adumbrated protocol; this is raw admission to the abstracts lines, and we charge booty affliction to assemble a allusive arresting ourselves, about creating an angel map of the abstracts curve over time:
Suppose we appetite to acquaint with a accessory that uses the SPI agreement (Serial Peripheral Interface, additionally sometimes alleged Microwire, ancillary consecutive or three- or four-wire serial, depending on the implementation). The adapted achievement would resemble the waveform in the analogy above: one achievement band provides a alarm signal, accession represents the abstracts $.25 (in accompany with the clock), and a third issues an end-of-data latch signal. If sending 8 $.25 of data, our achievement arrangement would allegation to be alert that admeasurement (to represent the aerial and low accompaniment of anniversary alarm tick), added two added bytes for the latch high/low at the end. 8 * 2 2 = 18 bytes in the achievement array (possibly a few added bytes, if a specific accessory requires a abbreviate adjournment afore the latch signal).
SPI ability be too abstruse for an anterior article; not anybody will accept the adapted apparatus around. Instead, let’s accomplish commodity visually gratifying: we’ll drive a accumulation of LEDs appliance beating amplitude modulation. This is of arguable account but it’s blatant and hints at the acceleration and accomplished ascendancy that’s accessible appliance this port.
The accouterments bureaucracy is agnate to the aboriginal example, but again four times: four LEDs, four 220 Omh resistors (we’re attached it to four in adjustment to assignment with the FTDI cable or SparkFun Basal Breakout, but it’s calmly abundant to eight with the added boards). The abrogating legs are all affiliated in accepted to the GND band (black wire on the FTDI cable), while the absolute legs are affiliated to CTS, TX, RX and RTS (brown, orange, chicken and blooming wires, respectively). The SparkFun Basal Blemish has DTR in abode of RTS for the aftermost pin, but the archetype cipher will assignment the aforementioned with either one…we’ll explain how shortly.
Here’s how the apparatus attending on a breadboard. Notice that the 5V band (red wire on FTDI cable) is skipped:
And here’s the antecedent code, appliance the D2XX API. Adapting this to libftdi is straightforward; see the aboriginal archetype for the altered syntaxes.
When auspiciously aggregate and run, the LEDs should boring drum in a repeating “chaser” cycle. There are some notable differences from the aboriginal example:
Pulse amplitude accentuation makes for a nice beheld affirmation of acceleration but abominably can’t absolutely be put to austere use. In accession to the previously-mentioned I/O latency, added accessories may be administration the USB bus, and the sum absolute is that we can’t calculation on this address to behave deterministically nor in realtime. PWM with an LED looks aloof accomplished to the eye…the timing is abutting enough…but aggravating to PWM-drive a servo is out of the question. For a ancillary consecutive agreement such as SPI, area a alarm arresting accompanies anniversary abstracts bit, this adjustment works perfectly, and hopefully that can be approved in a aftereffect article.
FTDI bitbang admission comes in accessible for abounding projects, but it’s not a band-aid to every problem. There are abounding situations area a microcontroller is still preferable:
We achievement this addition has buried the seeds of new hacks in your mind, or will breathe new activity into abandoned archetypal alongside anchorage hacks. To dig deeper, the FTDI web armpit is the best resource. Actuality you’ll acquisition abstracts sheets, articles, and best advantageous of all are the appliance notes. There’s additionally advice for alive with added languages: Java, Perl, Python and Beheld Basic, amid others.
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