Thursday, September 21, 2023
HomeTechnologyDIY Gamma-Ray Spectroscopy with a Raspberry Pi Pico

DIY Gamma-Ray Spectroscopy with a Raspberry Pi Pico

This text was first revealed as “The battle for the SX-70.” It appeared within the Could 1989 concern of IEEE Spectrum. A PDF model is offered on IEEE Xplore. The diagrams and pictures appeared within the unique print model.

But this sophisticated system had to slot in a bundle the scale of Land’s jacket pocket, he decreed—a constraint that meant using ICs. However as Polaroid couldn’t fabricate ICs, the success of its SX-70 undertaking lay within the fingers of outsiders.

The flash management contract was given to Common Electrical Co. Then in 1971, when GE dropped out of the IC enterprise, it was issued to Sprague Electrical Corp., in addition to to Fairchild Semiconductor Corp. of Palo Alto, Calif., and Texas Devices Inc. of Dallas, Texas. Solely Fairchild and Sprague ended up producing flash controllers.

Unbiased contracts to develop the motor and publicity management modules went to Fairchild and TI. The motor management module contained a linear management IC, an NPN motor drive transistor, and a discrete PNP dynamic braking transistor, and gave the designers little hassle. The publicity management module was a distinct story.

The grand problem

Included within the publicity management had been three ICs (early Fairchild variations had 4). The publicity timer used the present output of a silicon photodiode to manage how lengthy the shutter blades remained open. The delay-timing circuit generated 4 intervals: a delay of 40 milliseconds earlier than the shutter opened; the time the shutter remained open earlier than the flash was fired; the period of the flash; and the utmost publicity time given sure ambient lighting. The facility management IC drove the solenoids and motor management unit. And this all needed to match on a board that match right into a 27-by-95-by-2-millimeter house, minus a central gap for the digicam lens.

Electrical noise was a significant stumbling block. The photocell, as an example, working with as little as 15 picoamperes, needed to keep its state in an setting during which the motor, the solenoids, and the firing of the flash lamps drew amperes of present. Designers had been to take steps like inserting a delay between the discharge of the solenoids and the beginning of the photocell-timed publicity; redesigning circuitry on the facility provide line to reject noise from the motor; rising the voltage distinction between logic highs and lows, so noise spikes would not masquerade as bits; and together with a low-pass filter.

Because it was 1969, there have been no semicustom ICs, gate array know-how was in its infancy, and solely primitive packaging was out there—customary twin in-line packages (DIPs) had been no less than 0.125 inch thick—whereas logic and energy transistors couldn’t but share the identical piece of silicon. And Polaroid needed to purchase this publicity controller for US $5.75.

What pals are for

Polaroid chairman Land and TI chairman Patrick Haggerty had been previous pals. On a weekend journey a long time earlier than the SX-70 undertaking, they’d mentioned how electronics may someday make a very one-step digicam potential. The thought was to work on this dream collectively as quickly because the know-how arrived. So it got here as no shock when TI was charged with creating the digicam’s publicity management board. Land was relying on TI for a fail-safe design, based mostly on analog circuitry and confirmed know-how and due to this fact dependable, moderately priced, and able to being produced on schedule.

Polaroid additionally requested Fairchild, which it considered because the nation’s chief in IC know-how, to sort out a design that might push the state-of-the-art. Fairchild’s model was to be digital and extremely built-in, even to combining energy transistors with logic on one chip. To Polaroid the strategy seemed dangerous, however its engineers had been excited by its potentialities. Nonetheless, some inside Polaroid thought the Land-Haggerty relationship made nonsense of utilizing anybody however TI.

At midnight

The R&D contracts had been awarded in 1969, and the rivals went to work, each with the identical handicap: incomplete data. Fearing that Kodak Corp. may enter the moment digicam enterprise, Polaroid needed no leaks—a lot in order that it talked about neither the brand new movie nor the truth that at one level the digicam was redesigned as an SLR—and stored the design groups from seeing a prototype of the digicam. (Though TI’s then government vice chairman, the now-retired Fred Bucy, noticed an illustration of the early, non-SLR SX-70 in 1969, he mentioned nothing about it to the corporate’s engineers.) Stated Peter Carcia, an engineer on the SX-70 undertaking and nonetheless with Polaroid: “They’d little or no to work with”—solely stacks of specs.

white wiring diagram on blue-grey background with gates, outputs, and other features indicated, plus words "systems diagram M3 phase II G717566

When it contracted with Fairchild and TI to develop the electronics for the SX-70 digicam, Polaroid Corp. supplied this timing diagram together with 30 pages of different design specs, reliability necessities, and take a look at data. It signifies sequences of occasions for the 4 totally different modes of operation a totally computerized digicam required. Desk 1 signifies capabilities for taking pictures in ambient gentle, Desk 2 covers flash operation, Desk 3 calls out the sequence of occasions that’s triggered when a brand new movie pack is put in and its protecting cowl should be ejected, and Desk 4 describes the operations that happen when a pack of movie is used up.

Polaroid engineers recall that hundreds on the electronics had been described merely as inductive, and that particulars of the battery provide had been imprecise as a result of a brand new battery was being concurrently designed.

“We didn’t inform them whether or not a load on the electronics was from a solenoid or a relay, simply that it was an inductive load,” recollects Seymour Ellin, now a senior technical supervisor at Polaroid.

“Since we had been making our personal battery [designed concurrently], we couldn’t inform them what the battery provide could be,” mentioned Carcia. “I’d inform them ‘I need you to design a circuit, however I gained’t let you know what the facility supply will likely be,’ and they might have a look at me unusually.”

Polaroid needed no leaks—a lot in order that it talked about neither the brand new movie nor the truth that at one level the digicam was redesigned as an SLR.

Even worse was the “Y” delay—which Polaroid engineers instructed IEEE Spectrum got here from the “why” response given Fairchild and TI engineers at any time when they questioned one specification: the brief delay earlier than beginning the publicity, after the person pressed the button. This pause was to permit the mirror (which in an SLR digicam displays the picture seen via the lens to the viewfinder) to cease vibrating after it snapped out of the way in which of the movie to be uncovered. However that was greater than Polaroid needed to reveal. The sources of the noise downside had been left obscure, and its extent understated, mentioned Clark Williams, then a TI design engineer. “That motor pulled 3 amps of present and put out a wealthy spectrum of noise that performed havoc with our circuits,” he mentioned. (He’s now a design supervisor at Dallas Semiconductor Corp. in Dallas, Texas.)

The TI group, unable to base a breadboard on Polaroid’s diagrams alone, despatched two engineers and a number of other technicians to Cambridge to work in a bit of personal room there. Each time they wanted to check their breadboard, they’d hand it over to Polaroid engineers, who would carry it to a different room and ultimately report again that, say, a sure sign wanted adjustment or a sure part didn’t perform. The TI engineers would make a number of changes, then the breadboard was carried off for an additional take a look at. This to-and-fro-ing went on for six months, whereas, mentioned Michael Callahan, a senior TI design engineer who’s presently government vice chairman of engineering at Crystal Semiconductors Corp. in Austin, Texas: “We might have performed the work in two weeks if they’d allow us to signal nondisclosure agreements.”

Designing in Dallas

A preliminary spherical had disillusioned each IC groups. In 1969, earlier than Polaroid had firmed up many SX-70 particulars, it began each TI and Fairchild creating easy publicity management chips. This early effort, mentioned Polaroid engineers, was additionally used to develop and take a look at their working relationship with Fairchild. However the SX-70 undertaking modified a lot, notably with its redefinition as an SLR digicam, that Polaroid determined to begin over. Callahan and Ken Buss, now a senior member of the technical workers at TI, recall a gathering in Dallas at which the TI engineers proudly demonstrated the working circuits—solely to have Polaroid ignore them and announce its new necessities.

“That made our chips immediately out of date,” Buss mentioned. At Fairchild, too, enthusiasm flagged. Coincidentally, each corporations quickly after underwent a company restructuring, however whereas the modifications at Fairchild benefited its SX-70 group, these at TI practically value it all the pieces.

The TI designers, as a substitute of working immediately with Polaroid, had been instructed to report back to the Assembled Capabilities Group. Missing both chip growth or manufacturing amenities of its personal, the Group contracted with the IC designers’ division to develop three chips—a photocell amplifier to find out the proper publicity, a chip to regulate the motor and deal with dynamic braking, and a chip to deal with timing, depend the movie used, and serve different capabilities—and with one other division to fabricate the chips. The association additional filtered the already restricted data from Polaroid.

hand holding one circuit board between thumb and forefinger, two other circuit boards of similar size on table

Three totally different designs for the SX-70 publicity management electronics had been produced. Fairchild Semiconductor Corp.’s model (prime) went into cameras in 1972 and 1973—discover the polyimide movie used to connect the ICs to the board. Texas Devices Inc. produced its ceramic board (middle) throughout 1972, then redesigned, and gained the manufacturing contract away from Fairchild with a circuit board that used miniDIP IC packaging (backside).

That left the Group itself with the job of designing the circuitry that might tie the ICs collectively. Its engineers used 13 discrete transistors, 17 laser-trimmed thick-film resistors, and a photodiode, aspiring to mount them on a printed-circuit board. Administration as a substitute mandated a ceramic substrate basically as a result of, mentioned one TI design engineer, the Group reported to the identical supervisor as TI’s Hybrid Thick-Movie Group, which had extra capability.

“We knew we couldn’t meet the price targets with a ceramic substrate,” he mentioned. The ceramic, the dear metallic conductors, and the labor all value an excessive amount of for the substrate to function something greater than a prototype “to allow us to get all of the circuitry in a small space.” And when the design grew from 3/4 sq. inch to 4 or 5 sq. inches (from 5 to 25 or 32 sq. centimeters), the engineer recalled, he and the opposite designers predicted main manufacturing issues and urged doing a extra digital redesign with a printed-circuit board. However administration “wouldn’t pay attention,” he mentioned.

TI’s ceramic-based design did, nevertheless, carry out to Polaroid’s specs, and it went into manufacturing in late 1972. Nevertheless it was certainly a nightmare. First, at $100 a unit, it was nowhere close to the $5.75 value purpose. And manufacturing issues had been super, particularly with the large and due to this fact fragile ceramic substrate. As an illustration, mentioned TI design engineer Norm Culp: “We needed to take a chip, alloy it to a Kapton movie provider [a high temperature plastic foil], then wire bond the chip to the Kapton provider, then encapsulate the chip. The Kapton movie carriers had been then examined individually, then reflowed onto the ceramic substrate.”

Yield was about 1 p.c, and that one in 100 generally cracked on its option to Polaroid.

Furthermore, mentioned Culp, reflow-soldering chip carriers to the substrate induced microcracks within the ceramic, and for some time TI inspected each half for the issues. Then one engineer realized that heating your entire substrate as a substitute of simply the half to be reflow-soldered would cut back the microcracks, which, nevertheless, confirmed up in different components of the method. Yield was about 1 p.c, and that one in 100 generally cracked on its option to Polaroid.

Polaroid did order a number of hundred of those ceramic modules to get the SX-70 to market. Nevertheless it wasn’t in any respect proud of them. Stated Ellin, “TI, basically, failed to satisfy the price goal.”

Competing in California

In the meantime, engineers at Fairchild had been additionally working into difficulties, however technical ones solely. Early within the design course of, Fairchild’s company restructuring moved the R&D engineers out of their remoted laboratory into working divisions, making for higher communication with manufacturing, which “resolved loads of issues,” mentioned Howard Murphy, a senior member of the Fairchild analysis workers and the undertaking director for the SX-70 electronics.

“We designed a die that had round 20 flip-flops on it, in all probability a brand new excessive in IC complexity at the moment.”—Howard Murphy, Fairchild

One design downside was excessive temperature. Murphy recalled that the warmth of the heavy currents drawn by the motors and the solenoids affected the management logic circuitry, which then needed to be redesigned to work at greater temperatures—the specs indicated 40 °C. One other hurdle was the picture circuit. It needed to day trip after 20 seconds, in order that photos could possibly be taken in dim gentle of about 0.06 candela per sq. foot (0.65 candela per sq. meter), though the circuit design group wasn’t absolutely conscious of the explanation for this on the time. The circuit additionally needed to be very small and devour just some milliamperes. “So we designed a die that had round 20 flip-flops on it, in all probability a brand new excessive in IC complexity at the moment,” Murphy remembered.

Frank Perrino, a Fairchild product supervisor, first grew to become concerned within the SX-70 undertaking in Could 1971, when he oversaw its transfer into manufacturing. He recalled that the designers had been then engaged on 4 chips—a driver for the motor and solenoids, a timing chip, and the photodiode and photodiode amplification chips that later grew to become one bipolar CMOS IC. The cube had been to be mounted immediately on an irregularly formed 1-by-4-inch ceramic substrate beforehand metalized on either side with state-of-the-art strains and areas.

The prices concerned, nevertheless, dominated the strategy out for manufacturing, Perrino instructed Spectrum. “The ceramic and chips all needed to be excellent,” he mentioned, and there was zero “likelihood of this taking place.”

He concluded a printed-circuit board was a should, however the right way to mount the chips to it? Fairchild’s plastic DIPs had been too massive and dear for the job. He had, although, learn a paper by Common Electrical engineers on beam tape packaging (BTP), a forerunner of what’s now referred to as tape automated bonding (TAB). After investigating BTP, he instructed Fairchild and Polaroid administration, “If we don’t do it this manner, it’s not value doing.” Each agreed.

BTP employed reels of movie with copper traces laminated on it round preexisting holes. Chips with bumps of solder on their pads had been centered below the holes and bonded to the overhanging copper lead frames. Particular person die/movie modules had been then encapsulated, examined, clipped off the reel, and soldered to the circuit board.

Perrino laid out the double-sided printed-circuit board at dwelling on paper unfold throughout his pool desk. He then visited a number of corporations that made polyimide interconnect movie, contracted with 3M as a provider, and persuaded West-Bond Inc. of Anaheim, Calif., to construct tools for attaching the cube to the reel of laminated movie. The ultimate circuit board held three IC cube and two flip-chip, thick-film, laser-trimmed resistors.

Nevertheless, yields weren’t following the anticipated studying curve on two of the three ICs, the facility transistors due to excessive doping ranges and the timing chip as a result of, mentioned Perrino, of design errors. For instance, Jim Feit, one other engineer on the undertaking, recollects a parasitic machine affecting the flip-flops, which was mounted with the addition of a delay.

Nonetheless, although the components weren’t low-cost, costing Fairchild roughly $20 or $30 every, they had been manufacturable.


The SX-70 was launched in April 1972, together with the corporate’s annual stockholders’ assembly. A yr earlier, Land had teased the stockholders by pulling a prototype SX-70 out of his pocket and waving it within the air. That was a working mannequin, containing one in all TI’s first profitable ceramic circuit boards. However for this assembly, Polaroid wanted 20 cameras, and John Burgarella, now retired from the corporate, needed to make a number of journeys to Texas to hand-carry sufficient working boards again to Cambridge. A few month earlier, Land had introduced Fairchild engineers Perrino, Murphy, and Will Steffe to his Cambridge workplace and demonstrated the digicam to them. “It was clearly a technological breakthrough,” recalled Perrino, which motivated them “to return and make the factor work.”

u200bMan holds camera at chest level and waves photo above head with other hand

Edwin Land confirmed the primary working SX-70 digicam at a stockholders’ assembly in 1971. It was solely a prototype, and contained one of many first working ceramic circuit boards produced by Texas Devices. A TI engineer had put in it the night time earlier than the assembly, working with a digicam that was shrouded to stop him from studying something extra about it than he already knew.

The introduction went off with out a hitch. A few dozen scenes, from a poker recreation to a baby’s celebration, had been enacted in a big warehouse, and well-known photographers had been taking pictures them with the brand new cameras whereas Polaroid stockholders circulated and examined the photographs. Polaroid engineers had been additionally circulating, with further cameras of their pockets in case something went incorrect.

Resting on their laurels

So Fairchild gained a contract to fabricate the publicity management modules together with the motor circuits and the flash management circuits. The commerce press touted their victory. In line with a January 1973 Digital Information report, as an example, this contract, “believed to be the most important ever issued by a digicam producer to an electronics provider,” was value $19 million, and was “thought-about by some semiconductor executives as an omen of appreciable future enterprise.”

Fairchild disbanded most of its design group, happy with their success. However the manufacturing engineers pressed on, since the price of the product needed to be decreased by three-quarters or extra to satisfy Polaroid’s worth goal, and contract negotiations had been to be reopened for 1974. Nevertheless, mentioned Perrino, two of the chips within the publicity management module had been nonetheless in hassle.

C. Lester Hogan, who had just lately left Motorola Inc. to take over the Fairchild presidency, blames Fairchild’s then-outdated manufacturing amenities. He began a modernization, however he mentioned, “there wasn’t loads of further money,” and it was not full till someday in 1974.

Perrino blames the IC designs as nicely. “The design guidelines utilized in these chips had been touch-and-go with the know-how,” he instructed Spectrum. Polaroid’s Carcia agreed: ‘‘We had been pushing the basic know-how.” Redesigning the chips was talked about, however administration didn’t mandate it.

A matter of satisfaction

The TI design group was additionally disbanded in 1972. Some left the corporate, some moved on to different tasks. The failure, one design engineer instructed Spectrum, was a black mark that harm careers.

On the highest degree of TI, nevertheless, the guide was not being closed. TI chairman Haggerty reportedly referred to as his previous pal Land and mentioned, “We at TI don’t fail.” He assigned the undertaking about $540,000 from his personal funds, and instructed his managers to do no matter it will take to succeed. The code identify Venture Alpha emphasised the significance of the contemporary begin, and Haggerty put government vice chairman Bucy accountable for it.

The failure, one design engineer [said], was a black mark that harm careers.

As the unique TI group had been disbanded, Bucy deliberate to assemble one other one from the semiconductor division, and to make sure that this one would talk immediately with Polaroid and now have manufacturing obligations.

Dean Toombs, engineering director of the semiconductor group, held a sequence of conferences and developed a proposal for the redesign that was one other break with TI’s first strategy: it relied not on confirmed however on state-of-the-art IC know-how and packaging. A circuit board only one/64 inch thick was to carry as much as 4 digital (not analog) ICs and eight discrete elements at most. The chips could be floor mounted to the board in a miniDIP bundle, a technique of quantity meeting then new and dangerous however low-cost. (It’s now referred to as SOT, which stands for Small Define Transistors.)

The plan was authorised by Bucy, and Henri Jarrat (then Eljarrat) chosen to move the trouble. At first Jarrat objected to the project, however gave approach when instructed it was TI’s prime precedence. Given carte blanche to assemble a group from anyplace within the group, he stored the group manageably small—solely 18 folks. They rapidly partitioned the circuitry into three ICs and offered a six-month schedule for the redesign to Fred Bucy and Polaroid president William McCune.

Expert specmanship

Then Jarrat had his first assembly with Polaroid engineers. He instructed them he might solely combine the publicity management perform into three elements in the event that they waived a few of their specs. He started happening his listing and to every request the Polaroid engineers mentioned no. So Jarrat stood up, threw his papers down, and mentioned, he recalled, “Now I do know why this undertaking goes nowhere. This can by no means work, and I don’t wish to have my identify hooked up to a failure.” He charged out of the room. Toombs backed Jarrat’s menace. “We needed to get the shopper below management,” he instructed Spectrum.

The power to barter was partly additionally as a result of availability of working cameras to review and the development of a prototype on which to check breadboards of the chips—luxuries denied the primary TI group.

After a quick adjournment, the assembly was reconvened and from then on Polaroid negotiated specs. For instance, the 20-second day trip, for taking an image in a dimly lit room, had made the sign from the photodiode impossibly low for the primary design groups and this time round was reduce to 10 seconds. “The massive cause for our success was Jarrat’s success at convincing them to ease the specs,” mentioned Clark Williams, a member of the second group.

The power to barter was partly additionally as a result of availability of working cameras to review and the development of a prototype on which to check breadboards of the chips—luxuries denied the primary TI group. And when the primary group did increase questions out of concern for manufacturability, recalled Buss, the one TI engineer to work on each the design and the redesign efforts, they had been instructed, “Effectively, your competitors can do that.” And, in actual fact, Fairchild engineers don’t recall that the specs had been problematical.

TI started producing the Venture Alpha boards in amount in mid-1973.

table listing part types and quantities

With the redesign, TI quoted Polaroid a worth of about $4.10 a unit—nicely under the $5.75 goal. Stated former Fairchild president Hogan: “On the time, it value us $10. We actually believed we might get it to $6, however when TI bombed the worth down to 2 thirds of the goal worth, we simply needed to drop out.” As for a redesign, mentioned Hogan, “we didn’t have the cash to take a position that approach—we needed to spend money on the generic fixing of the manufacturing facility.”

TI created a particular digicam division with Polaroid as its solely buyer. The corporate made about 850 000 items in 1974 and continued to provide the design till the SX-70 and the SX-70 Mannequin 2 had been discontinued in 1977. It additionally spun off a number of improvements, together with packaging for TI’s watch shows. And the engineers on the Venture Alpha group had been rewarded with then substantial raises of $100 to $500 a month.

West-Bond and 3M, corporations Fairchild had recruited to fabricate packaging tools and movie tape, continued to profitably produce them for different corporations.

Fairchild used the BTP packaging know-how it developed for the SX-70 on its high-volume plastic DIP merchandise at a number of manufacturing amenities. It additionally took its digicam management know-how abroad on a tour of Japanese digicam producers, however after a number of unsuccessful months gave up and closed down the manufacturing line for the publicity management module. It continued to fabricate flash management modules for Polaroid for an additional yr, nevertheless. Inside six months to a yr of dropping the publicity management contract, no less than half the individuals who had labored on the undertaking moved to different corporations, Feit recalled.

Completely happy ending

Might the design have gone extra easily? Actually higher communications between Polaroid and the 2 semiconductor corporations and amongst totally different divisions inside TI and Fairchild would have eradicated a few of the tough spots.

From Polaroid’s standpoint, the data it handed out was as full because it could possibly be. In any case, a number of components of the digicam system had been being developed concurrently, in order that the system specs couldn’t in the meantime be finalized. Additionally, mentioned one Polaroid engineer, unfamiliarity with images impaired the IC designers’ comprehension of the info they got.

Within the eyes of the TI and Fairchild engineers, helpful data was withheld, and Polaroid engineers do admit a preoccupation with secrecy.

Nonetheless, within the eyes of the TI and Fairchild engineers, helpful data was withheld, and Polaroid engineers do admit a preoccupation with secrecy attributable to concern over competitors from Kodak. Maybe being instructed that sure design points had but to be resolved or an in depth rationalization of how an SLR capabilities would have elicited extra inventive engineering from the IC designers.

Be that as it might, the SX-70 was a superb success. Polaroid bought some three million items of the leather-covered Mannequin 1 with its chrome-plated trim and the plastic-bodied Mannequin 2. (Mannequin 3, launched in 1975, was not an SLR.) So whereas the design issues each TI and Fairchild endured triggered tense moments in any respect three corporations, their answer opened up an enormous new client market in electronics.

To probe additional

For particulars on the SX-70 circuitry, see “Behind the lens of the SX-70,” by Gerald Lapidus, IEEE Spectrum (December 1973, pp. 76-83).

Each Time and Life magazines featured the SX-70 digicam on their covers in 1972, and mentioned it in “Polaroid’s Large Gamble on Small Cameras” (Time, June 26, 1972, pp. 80-82) and “If you’ll be able to state an issue, it may be solved” (Life, October 27, 1972, p. 48). To know how the event of the SX-70 match into Polaroid’s Jong historical past, learn The On the spot Picture: Edwin Land and the Polaroid Expertise by Mark Olshaker (Stein & Day, New York, 1978).

Frank Perrino’s model of tape automated bonding is described in U.S. Patent #3,868,724, “Multi-layer connecting constructions for packaging semiconductor gadgets mounted on a versatile provider,” dated Feb. 25, 1975.

From Your Web site Articles

Associated Articles Across the Internet



Please enter your comment!
Please enter your name here

Most Popular

Recent Comments