ornitz@kodak.UUCP (barry ornitz) (01/06/89)
In article <888@ubu.warwick.UUCP> haldane@uk.ac.warwick.cs (Steve Sykes) writes: >The light detection devices they use are ordinary 8 pin dil packages >that are made from transparant plastic - so why, I think to myself, could one >not package other chips in the same way? It looks really neat. Ok, >maybe light would affect them, but you could do different colours - blue >for ttl, red for cmos etc - why not even colour code chips in stripes in >the same way resistors are? > >Thinking it over, it ocurred to me that someone must have already thought of >doing it, and so there must be a good physical reason for not doing it. >But I'm not really sure what this might be - surely not just the price of >the dye? Light does affect many chips creating surface charge carriers. I have even seen circuits where the leakage current caused by light in glass encased small signal diodes (1N914, 1N4148) caused erratic behavior. I even saw a RAM chip used as the basis for a video camera - someone had cut the top off the ceramic package and discovered the effect by accident. The results were crude with essentially infinite contrast (black or white, no gray) and poor light sensi- tivity but it did work. I have some vintage Westinghouse chips someplace in the junque bin that are blue and some beautiful pink ceramic chips from TI in a DIP package with gold-plated, brazed-on leads. Heck, I still have a pile of germanium parts! The chip packages are colored with a pigment rather than a dye. It takes very little carbon black to get a black or dark gray epoxy; it takes a lot more of any other color pigment, usually with titanium dioxide. If you sell a part for ten cents, you don't want to spend another half cent on color - carbon black is _very_ cheap and much of the plastic is filler anyway. Color coding for numbering chips is also expensive - lots of numbers and how do you have room for the date code, lot number, the manufacturers logo and the made in Malaysia disclaimer? ;-) 73, Barry WA4VZQ ----------------- | ___ ________ | | | / / | | Dr. Barry L. Ornitz UUCP:..rutgers!rochester!kodak!ornitz | | / / | | Eastman Kodak Company | |< < K O D A K| | Eastman Chemicals Division Research Laboratories | | \ \ | | P. O. Box 1972 | |__\ \________| | Kingsport, TN 37662 615/229-4904 | | ----------------- And I did hug my cats today - all 10; but I only shake hands with the 5 dogs.
wwg@brambo.UUCP (Warren W. Gay) (01/09/89)
In article <1590@kodak.UUCP> ornitz@kodak.UUCP (barry ornitz) writes: >In article <888@ubu.warwick.UUCP> haldane@uk.ac.warwick.cs (Steve Sykes) writes: >>...maybe light would affect them, but you could do different colours - blue >>... > >Light does affect many chips creating surface charge carriers. I have even >seen circuits where the leakage current caused by light in glass encased small >signal diodes (1N914, 1N4148) caused erratic behavior. I even saw a RAM chip >used as the basis for a video camera - someone had cut the top off the ceramic >package and discovered the effect by accident. The results were crude with >essentially infinite contrast (black or white, no gray) and poor light sensi- >tivity but it did work. >... When I was much younger (IBM-1130 days :-), I used to take apart the replaced circuit boards from the "1130", and take the metal sheilds off the top of the square "integrated" circuit "chips". The "integrated" circuits of that era were big enuf that you didn't need a microscope to figure out the chip design... and I used to try to get them to work - with the covers off! I realized a few years later why I could never get the suckers to work, when I started to play with light sensitive transistors :-)! I don't hug my cats... Three is too many to hug... I kick them, its more conveniant! :-) 73s de VE3WWG (Warren)..............LSI represents Large Scale Investment, .................transistors are "discrete", but tubes are just plain fun. ................Bramalea Software Systems Inc...!utgpu!telly \ !brambo!wwg ...................!{uunet!mnetor, watmath!utai}!lsuc!ncrcan / -- 73s de VE3WWG (Warren)..............LSI represents Large Scale Investment, .................transistors are "discrete", but tubes are just plain fun. ................Bramalea Software Systems Inc...!utgpu!telly \ !brambo!wwg ...................!{uunet!mnetor, watmath!utai}!lsuc!ncrcan /
abali@phao.eng.ohio-state.edu (Bulent Abali) (01/11/89)
>>Light does affect many chips creating surface charge carriers. I have even >>seen circuits where the leakage current caused by light in glass encased small >>signal diodes (1N914, 1N4148) caused erratic behavior. I even saw a RAM chip Back in the old times when phototransistors were expensive, I would saw off the top of the metal case of a regular transistor with a file, and that would give me a pretty good phototransistor. -=- Bulent Abali Ohio State Univ., Dept.of Electrical Eng. 2015 Neil Av. Columbus, Ohio 43210 abali@baloo.eng.ohio-state.edu