fit your needs. It was 100,000 -ohms in the author's model giving him a minimum time HOUR MASTER delay of 30 seconds. Capacitor Cl may also be changed in value to modify the sized 200 uF timing capacitor. The sche- delay time. With a 200 uF capacitor and matic shows how it's done. Diac D1 and a 10 megohm pot, the maximum delay is Triac Q3 form a standard AC phase con- well over an hour and over a half -hour trol which can be turned off through the with a 5 megohm pot. contacts of relay K1. For use as a speed Getting Busy. The author's model was control, R4, a 250,000 -ohm linear pot, is housed in a 61/4 -in. x 33ús -in. x 17A3 -in. added as shown to points A and B. With plastic case with an aluminum panel used mode switch S3 in the out position. you as the top plate of the unit. You may have a regular speed control. When battery want to start by drilling holes in the cover switch S2 is closed, the timing circuit is for switches, pot(s), and socket. Be sure t armed. By pressing time -start switch S1, to add an extra hole for potentiometer R4 timing capacitor Cl is charged by the bat- if you want the speed control feature. tery; when Si is released, Cl slowly dis- Go to work on the circuit board; you charges through time -set pot R1 and can use about a 2 -in. x 41/2 -in. piece of source -follower Q1. perforated phenolic board. Wiring is Time-set potentiometer R 1 can be either straight -forward, but keep the triac 5 or 10 megohms. Resistor Rx sets the low circuitry and the FET at opposite ends of limit of the timer and may be selected to (Continued on page 93) unmuumnmuunnmunmummummuuuuummuunmuwumnuuuummmuwunmuuuuuumuuummuuuuumuummuummumimmwuuuuuuuuumnnunumuumuum PARTS LIST FOR HOUR MASTER B1 -9 -volt battery, Eveready 216 or equiv. Rl -5 megohm to 10 megohm, linear taper po- C1 -1 to 1000 uF, 12 -VDC electrolytic capacitor tentiometer (see text) (see text) R2- 2,700 -ohm. 1/2-watt resistor, 10% C2 -0.05 uf, 600V disc capacitor R3- 120,000 -ohm, 'h -watt resistor, 10% (see C3-0.1 uF, 600V disc capacitor text) D1 -Diac, Motorola HEP -31 1 S1 -SPDT pushbutton switch (Switchcraft 1002 Kl -Sensitive SPDT relay (Potter & Brumfield or equiv.) (time -start switch) type 1M5 or equiv.) (see text) S2 -SPST toggle switch (power switch) 01-N- channel FET, Motorola HEP -801 S3 -SPDT toggle switch (mode switch) Q2 -NPN transistor, Motorola HEP -55 5O1 -AC receptacle, chassis mount Q3- Triac, RCA 40429 Misc.- Hardware, knobs, perforated board, flee Rx- 100,000 -ohm, 1/2-watt resistor, 10% clips, wire, solder, etc. MODE ,BI 52 SWITCH R4 if = OUT 9VDC ÓFF-ONON 250K TIME START (PUSH BUTTON) al g SI HEP -801 (SEE CI TEXT) 200uF RX (SEE TEXT) NOTE: e b c g TI REMOVE JUMPER SOI BETWEEN A B B T2 AND INSERT R4 (CASE) FOR SPEED CASE CONTROL /LAMP DIMMER MODIFICATION. HEP -801 HEP-55 40429 mmnummummuunuuuuuummiinmmnmmpnunnuunmuuumuuuuuwuuuumuwmuummuunqu+ mununuummuuunumuuununmuuumuumumuuuuuuunuuuwr. 58 ELEMENTARY ELECTRONICS .