Radio Technique George M Myers ONE OF THE genuinely ubiquitous fallouts space program LED semiconductor emits light within its crystal structure differentiated incandescent lamp emits light surface hot metal wire Most portable cal culators display results red numbers made up series tiny red spots spots LED Try read calcu lator bright sunlight discover main drawback LEDthey arent very bright can work around problem find group significant advantages Small size lightweight long life low voltage current requirements also very voltage sensitive Fig leads thoughts using voltmeters purpose checking state charge transmitter receiver battery packs Several manufactur ers offer devices exactly purpose fore looking lets learn lit tle about LED thing LED available colors Red orange yellow green com mon Without going physics device lets state color function alloy used make device Red devices emit lowest voltages typically 17 Volts 20 milliamps 250C Green devices require around 22 Volts orange yellow require approximately 2 volts run down local Radio Shack similar electronic parts retailer will find LED marked 5VDC I2VDC etc devices fabricated internal voltage-dropping resistors somewhat less voltage-sensitive Fig 2 light emitting junction will encapsu lated colored transparent plastic may clear point-source LED filled diffusing material area-source diffused LED Point-source LED bright er diffused type can easier eyes some conditions simplest form can connect series LED make device will lighted voltage range 4 6 volts dark range 0 4 volts Fig 3 series re sistor 10 100 ohms iA watt chosen limit current 6 volts 50 ma less LED doesnt light reverse battery connections POWER-CYT offered CYT-4 Industries Oak Park Ill type uses red LED have purchased Eastern States R/C Jamboree WRAMs show March 1975 have used through summer performs advertised deducts very little power supply Mount under wing some other shady spot order get definitive indication battery exhaustion S L CORLEY Gadg Ct Man Central Jersey RC Club writing March 75 issue club newsletter Hadley Airmail offered circuit holds LED until voltage drops pre-selected critical value time LED flashes rate 45 flashes per minute alert problem built son Christo pher has used summer long also works should net effect using devices have found can fly confidence weather changes suddenly leaves us no time recharge Some day soon Ive got try quick charter Try youll like Fig 4 Ace R/C Inc uses LED replace output meter its new 7-channel digital com mander transmitter kit application LED driven type 555 IC chip instead UJT used S J CORLEY func tion same transmitter battery pack voltage drops below pre-selected value LED flashes rapidly about 4 pulses per sec ond LED recessed piece tubing make visible bright sunlight worked reasonably well sample examined LED provides simple durable voltagesensitive pilot light radio system Try others available have mentioned see obtain benefits Chris have address 70 Froehlich Farm Rd Hicks ville NY 11801 January 1976 9 RED ORANGE 20 OW GREEN 0 0 OLTS FIGURE 1 TYPICAL LED CHARACTERISTICS Allan Johncock Texas City Texas assisted son Mike attaching wing pattern job won B Pattern Nats Ron Van Putte photo p OC m 82K 82 UJE CoUJT OH1N400981 z 8MFII Hiovuc- LEO OA VOLTS UJTRadio ShackI7N 82 part 276-ill eqoinaleetUJTK part 276-026L.I781 LEORadio Snack equivalent LookinS pins lOOK potentiometer can replaced cuith fixed 1K resistor -- leg appropriate fiend resistor about 47K leg selected start flashing 44 colts can constructed 3/8 n 1 3/8 perf board less $5 FIG 4- CRITICAL VOLTAGE INDICATOR SL CORLEY 48VDc Tmo GREEN LEO 10 100 ohms required 1/4 mast -VOLTS connect unused channel receicer side pomer smitch harness Attach smiich mith GE CLEARSEAL FIG 3-VOLTAGE-SENSITIVE PILOT LIGHT 0 H 115/1 [Jk c2O 0 036 91215 VOLTS FIGURE 2 TYPICAL RESISTOR LED CHARACTERISTICS