Strong building and construction, classy style, and high-precision result. In the past, Hewlett-Packard made test-and-measurement devices that was cherished by functioning designers. Certain, go down among those infants on your foot and you were taking a look at a busted toe. Yet that’s a tiny cost to spend for integrity and some personality structure. So when I just recently encountered a very early 1970s HP 7041A X-Y recorder while removing my moms and dads’ attic room, I understood that I simply needed to see if I might obtain it up and running once more.
What is the distinction in between an X-Y recorder and a plotter?
X-Y recorders were developed to chart information from analog tools in genuine time, instead of plotters, which outline the results of electronic computer systems. The fundamentals coincide: There’s a system to elevate and decrease a pen, and electric motors to relocate the pen throughout the surface area of a web page. The large distinction is that a plotter generally makes use of electronic commands to manage the pen’s movement, while the movement of a recorder’s pen is regulated by analog voltage inputs.
So all I required to do was feed the HP recorder the ideal voltages, and I might attract anything I desired! Just a few challenges stood in my means.
The recorder user interface permits Python code created on a Raspberry Masterpiece [bottom right] to produce analog signals that are degree moved backwards and forwards to fulfill the various arrays needed by the plotter’s x- and y- axis. James Provost
The very first barrier was obtaining things home, since my moms and dads’ attic room remained in Ireland and suitable a 13-kilogram, 48-by-36-by-17-centimeter leviathan right into my luggage for my trip back to New York City had not been occurring. Concerning United States $300 in packaging products and delivery costs addressed that trouble, and I was still a little successful monetarily contrasted to getting a comparable vintage recorder from ebay.com, and means in advance of getting a brand-new Bantam Equipment NextDraw plotter with a comparable illustration location. (To be reasonable to Bantam, its plotters are streamlined plug-and-play gadgets that can deal with a much broader variety of pens).
The 2nd barrier was that the recorder really did not function. As soon as I obtained it home, I found that the y– axis might be changed by hand utilizing a handle on the control board, yet the x– axis was dead. The system for increasing and decreasing the pen made a weak clunking noise and hardly jerked.
” Had I simply invested a great deal of cash to deliver home an HP-model watercraft support?”
I opened the situation, which fasted deal with a Phillips screwdriver– no odd protection screws, no adhesive, no vulnerable plastic, no yellow sticker labels alerting that your service warranty would certainly be nullified and you ‘d possibly obtain boils if you risked to look within. On the perfectly outlined published circuit card within, I detected some resistors that were plainly not component of the manufacturing facility mount. Were they alterations or fixings? If the last, had they achieved success or had I simply invested a great deal of cash to deliver home an HP-model watercraft support? And I had no concept just how the 40-pin user interface adapter on the back of the recorder was meant to be linked to manage signals.
All these issues were addressed when I located the recorder’s guidebook on ebay.com. Oh, what a handbook. Not simply running directions, yet in-depth images for taking the recorder totally apart and placing it back with each other. It noted every part, with pictures of the circuit card and digital schematics on gatefolds. And it consisted of instructions for changing the wiring if you intended to determine various voltage arrays than the manufacturing facility setups– remove a resistor below and there and solder in some brand-new ones. This described the resistors I would certainly detected. In a globe where licenses and software program locks forbid folks from simply plugging in a replacement component, the idea of a significant firm motivating its consumers to burst out a welding torch is mind boggling.
Quickly, the application of some instrument oil, silicone grease, and Kimwipes had the x– axis and pen lifter functioning once more. I linked a variable power supply to the recorder’s adapter and gradually brought the voltage up as I enjoyed the pen owner relocate reaction. This permitted me to figure out the recorder’s input arrays, which ended up being 0 to 1 volt for the y– axis, and 0 to 5 V for the x– axis, covering 25 and 38 centimeters of movement, specifically, with around 0.2 millimeter precision.
The following action was to develop a user interface. Although microcontrollers typically have digital-to-analog abilities integrated, there’s typically just one real analog result pin. I required 2. A strategy like pulse-width modulation would certainly allow me result an analog-ish voltage on numerous pins, yet generally with only 8-bit resolution or 256 unique voltage degrees. I required at the very least 1,900 degrees to match the recorder’s precision.
The Raspberry Masterpiece makes use of a growth “HAT” and 2 12-bit digital-to-analog converters regulated by means of I2C ports to produce 0- to 3.3-volt control signals. These are moved to 0- to 1-V and 0- to 5-V arrays utilizing a voltage divider panel and amplifier specifically, in addition to a reasoning gateway utilized to transform a 3.3-V electronic signal that elevates and decreases the pen to a 5-V degree. James Provost
So I purchased 2 $5 Adafruit MCP4725 breakout boards These are 12-bit digital-to-analog converters– each offering 4,096 unique degrees– regulated over an I2C serial link, and 2 boards can share the exact same I2C bus. I linked them to a Raspberry Pi Model B+ I spied of a cabinet by means of a $6.60 SparkFun Qwiic HAT
The DACs produced a signal in the variety of 0 to 3.3 V, so I sent out one board’s result via a voltage divider to scale it to 0 to 1 V for the y– axis. For the x– axis, I fed the various other board’s result via an LMC6484 amplifier, powered by a 5-V pin from the Masterpiece, to bring it approximately 0 to 4.8 V– not rather the complete variety, yet it’ll do till I think of a much more advanced user interface. I brought a signal to elevate and decrease the pen out from among the Masterpiece’s GPIO pins, passing it via a 74LS08 AND gate IC utilized as an economical and joyful 3.3- to 5-V electronic degree shifter.
I after that composed code on the Masterpiece to place the plotter via its rates, utilizing parametric formulas created in CircuitPython to attract swirling hypotrochoids and various other geometric contours. Inevitably, it must be feasible to have the Masterpiece approve and convert commands created in a plotter-control language such as HP-GL After that I’ll have the ability to story vector graphics and message from attracting software program like Inkscape But also for currently, I enjoy to simply have my recorder humming away close to me, hale and hearty and constructed to last.
发布者：Stephen Cass，转转请注明出处：https://robotalks.cn/reviving-a-1970s-analog-hp-x-y-recorder/
