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DIY Gamma-Ray Spectroscopy with a Raspberry Pi Pico

This text was first printed as “The battle for the SX-70.” It appeared within the Might 1989 concern of IEEE Spectrum. A PDF model is accessible 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 venture lay within the palms of outsiders.

The flash management contract was given to Basic 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.

Impartial 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 unique 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 control 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 length of the flash; and the utmost publicity time given sure ambient lighting. The ability 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 area, 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 preserve 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 ability provide line to reject noise from the motor; rising the voltage distinction between logic highs and lows, so noise spikes would now not masquerade as bits; and together with a low-pass filter.

Because it was 1969, there have been no semicustom ICs, gate array expertise was in its infancy, and solely primitive packaging was out there—commonplace 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 wished to purchase this publicity controller for US $5.75.

What pals are for

Polaroid chairman Land and TI chairman Patrick Haggerty had been outdated pals. On a weekend journey a long time earlier than the SX-70 venture, they’d mentioned how electronics may someday make a really one-step digicam potential. The thought was to work on this dream collectively as quickly because the expertise 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, primarily based on analog circuitry and confirmed expertise and subsequently dependable, moderately priced, and able to being produced on schedule.

Polaroid additionally requested Fairchild, which it seen because the nation’s chief in IC expertise, to sort out a design that might push the cutting-edge. Fairchild’s model was to be digital and extremely built-in, even to combining energy transistors with logic on one chip. To Polaroid the method appeared 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 nighttime

The R&D contracts had been awarded in 1969, and the opponents went to work, each with the identical handicap: incomplete info. Fearing that Kodak Corp. may enter the moment digicam enterprise, Polaroid wished 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 vp, 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.) Mentioned Peter Carcia, an engineer on the SX-70 venture and nonetheless with Polaroid: “That they had 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. offered this timing diagram together with 30 pages of different design specs, reliability necessities, and take a look at info. It signifies sequences of occasions for the 4 totally different modes of operation a completely computerized digicam required. Desk 1 signifies features for taking images 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 have to 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 obscure 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 might inform them ‘I need you to design a circuit, however I received’t inform you what the ability supply will probably be,’ and they might have a look at me surprisingly.”

Polaroid wished 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 informed IEEE Spectrum got here from the “why” response given Fairchild and TI engineers each time they questioned one specification: the quick delay earlier than beginning the publicity, after the consumer 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 best way of the movie to be uncovered. However that was greater than Polaroid wished to expose. The sources of the noise drawback 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 crew, 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 non-public room there. At any time when 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 couple 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 vp of engineering at Crystal Semiconductors Corp. in Austin, Texas: “We might have accomplished the work in two weeks if they’d allow us to signal nondisclosure agreements.”

Designing in Dallas

A preliminary spherical had upset 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 venture modified a lot, notably with its redefinition as an SLR digicam, that Polaroid determined to start out over. Callahan and Ken Buss, now a senior member of the technical employees 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 adjustments at Fairchild benefited its SX-70 crew, these at TI practically price it all the things.

The TI designers, as an alternative of working immediately with Polaroid, had been informed to report back to the Assembled Capabilities Group. Missing both chip growth or manufacturing services of its personal, the Group contracted with the IC designers’ division to develop three chips—a photocell amplifier to find out the right publicity, a chip to regulate the motor and deal with dynamic braking, and a chip to deal with timing, rely the movie used, and serve different features—and with one other division to fabricate the chips. The association additional filtered the already restricted info 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 (high) 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 received 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, desiring to mount them on a printed-circuit board. Administration as an alternative 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 associated fee objectives with a ceramic substrate,” he mentioned. The ceramic, the valuable metallic conductors, and the labor all price 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 hear,” he mentioned.

TI’s ceramic-based design did, nonetheless, 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 price objective. And manufacturing issues had been great, particularly with the big and subsequently fragile ceramic substrate. As an example, 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 typically cracked on its strategy 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 all the substrate as an alternative of simply the half to be reflow-soldered would scale back the microcracks, which, nonetheless, confirmed up in different components of the method. Yield was about 1 p.c, and that one in 100 typically cracked on its strategy 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. Mentioned Ellin, “TI, basically, failed to satisfy the associated fee goal.”

Competing in California

In the meantime, engineers at Fairchild had been additionally operating 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 a whole lot of issues,” mentioned Howard Murphy, a senior member of the Fairchild analysis employees and the venture director for the SX-70 electronics.

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

One design drawback 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 increased temperatures—the specs indicated 40 °C. One other hurdle was the picture circuit. It needed to trip after 20 seconds, in order that photos might be taken in dim gentle of about 0.06 candela per sq. foot (0.65 candela per sq. meter), though the circuit design crew wasn’t absolutely conscious of the rationale for this on the time. The circuit additionally needed to be very small and eat only a few milliamperes. “So we designed a die that had round 20 flip-flops on it, most likely a brand new excessive in IC complexity at the moment,” Murphy remembered.

Frank Perrino, a Fairchild product supervisor, first turned concerned within the SX-70 venture in Might 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 turned 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 each side with state-of-the-art strains and areas.

The prices concerned, nonetheless, dominated the method out for manufacturing, Perrino informed Spectrum. “The ceramic and chips all needed to be excellent,” he mentioned, and there was zero “likelihood of this occurring.”

He concluded a printed-circuit board was a should, however how one can mount the chips to it? Fairchild’s plastic DIPs had been too massive and expensive for the job. He had, although, learn a paper by Basic Electrical engineers on beam tape packaging (BTP), a forerunner of what’s now referred to as tape automated bonding (TAB). After investigating BTP, he informed Fairchild and Polaroid administration, “If we don’t do it this fashion, it’s not price 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 beneath 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.

Nonetheless, yields weren’t following the anticipated studying curve on two of the three ICs, the ability 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 venture, recollects a parasitic system affecting the flip-flops, which was fastened 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, along side 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 certainly one of 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 forestall him from studying something extra about it than he already knew.

The introduction went off and not using a hitch. A few dozen scenes, from a poker recreation to a toddler’s birthday celebration, had been enacted in a big warehouse, and well-known photographers had been capturing 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 fallacious.

Resting on their laurels

So Fairchild received 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 keeping 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 price $19 million, and was “thought of by some semiconductor executives as an omen of appreciable future enterprise.”

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

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

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

A matter of delight

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

On the highest degree of TI, nonetheless, the e book was not being closed. TI chairman Haggerty reportedly referred to as his outdated buddy Land and mentioned, “We at TI don’t fail.” He assigned the venture about $540,000 from his personal finances, and informed his managers to do no matter it will take to succeed. The code identify Undertaking Alpha emphasised the significance of the recent begin, and Haggerty put government vp Bucy in command of it.

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

As the unique TI crew 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 still 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 method: it relied not on confirmed however on state-of-the-art IC expertise and packaging. A circuit board only one/64 inch thick was to carry as much as 4 digital (not analog) ICs and eight discrete parts at most. The chips could be floor mounted to the board in a miniDIP bundle, a way 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 accepted by Bucy, and Henri Jarrat (then Eljarrat) chosen to move the hassle. At first Jarrat objected to the task, however gave means when informed it was TI’s high precedence. Given carte blanche to assemble a crew from anyplace within the group, he stored the group manageably small—solely 18 individuals. They shortly 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 informed them he might solely combine the publicity management perform into three parts 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 venture goes nowhere. This may by no means work, and I don’t need to have my identify hooked up to a failure.” He charged out of the room. Toombs backed Jarrat’s risk. “We needed to get the shopper beneath management,” he informed Spectrum.

The power to barter was partly additionally because of the 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 crew.

After a quick adjournment, the assembly was reconvened and from then on Polaroid negotiated specs. For instance, the 20-second 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 purpose for our success was Jarrat’s success at convincing them to ease the specs,” mentioned Clark Williams, a member of the second crew.

The power to barter was partly additionally because of the 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 crew. And when the primary group did elevate 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 informed, “Properly, your competitors can do that.” And, actually, Fairchild engineers don’t recall that the specs had been problematical.

TI started producing the Undertaking 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—effectively under the $5.75 goal. Mentioned former Fairchild president Hogan: “On the time, it price 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 means—we needed to put money into 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 couple of improvements, together with packaging for TI’s watch shows. And the engineers on the Undertaking Alpha crew 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 expertise it developed for the SX-70 on its high-volume plastic DIP merchandise at a number of manufacturing services. It additionally took its digicam management expertise 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, nonetheless. Inside six months to a yr of shedding the publicity management contract, no less than half the individuals who had labored on the venture moved to different corporations, Feit recalled.

Completely happy ending

May the design have gone extra easily? Definitely 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 might 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 info was withheld, and Polaroid engineers do admit a preoccupation with secrecy.

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

Be that as it could, the SX-70 was a superb success. Polaroid offered 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 resolution opened up an enormous new shopper 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 Massive 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 grasp how the event of the SX-70 match into Polaroid’s Jong historical past, learn The Instantaneous 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 units mounted on a versatile provider,” dated Feb. 25, 1975.

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