When I tried LOADing my first program on my ZX80, I was excited. This excitement quickly changed to disappointment after my fifth or sixth attempt. Finally after several more tries, the program was LOADed. I marked the volume control. By the time I had loaded two or three more programs it was evident that even with a marked volume control, LOADing would and could still be difficult.
In searching for a better method, I came across an article in SYNC on using an LED for a loading monitor attached to the ZX80 internally.
If an LED could work inside, why not outside? Further study and experimentation proved that it could work! Externally mounted—the monitor was easy to alter, experiment with, and throw away if it proved unreliable. Also my ZX80 would not have to suffer unnecessary exposure of its vital parts if it did not have to be opened.
The monitor consists of two LEDs, a diode, some wire, and a case to house everything. The number 1 LED acts as an indicator of too low a volume or of the correct volume. The number 2 LED is an indicator of volume which is too loud.
To use the monitor, you should set your tape recorder to the portion just prior to the actual program. Plug the monitor into the earphone of the recorder, but do not plug into the ZX80 yet. Play the program. Watch the LEDs. The number 1 LED will glow brightly when the volume is correct; it will not light or it will barely flicker when the volume is too low. If the second LED is lit or flickering then the volume is too high for loading. When the monitor is adjusted so that only the number 1 LED is glowing brightly, rewind the tape, plug into the ZX80, and LOAD!
Parts Needed (Radio Shack part numbers)
- 2 Subminiature LEDs # 276-1123
- 1 Micro miniature diode # 276-1104
- 1 piece of dual speaker wire
- 2 pieces of wood
To build the monitor, you need the items listed on the diagram (or equivalent). All of these items can be purchased at electronics supply houses. (As a point of reference, I have given the Radio Shack numbers.) Now decide which of the plugs on the loading cable you want to use for attaching your monitor. Unscrew the plastic cap (do not unhook any wires) and expose the two prongs inside. The long prong of the plug is the grounded side which I have labelled as “B” in the diagram. “B” is also the marking for the short lead of the LED (cathode side). Cut a piece of speaker wire about 3 to 6 inches long (the length is up to you). After stripping the two wires on one end, insert the wire through the back of the plastic cap of the plug in the same manner as the cable is inserted. Solder one wire to the short prong of the plug and the other wire to long prong (as illustrated). Now solder “A” wire to the long lead of the LED. Solder the other wire to the short lead (you may decide to shorten both the leads, so remember to keep track of the cathode which is to be connected to “B” wire). Solder the long lead of number 2 LED to the long lead of number 1 LED. Now solder the diode to the short lead of number 1 LED (make sure the cathode side is soldered to this lead—usually a color band indicates the cathode end). Connect other end of the diode to the remaining lead of the number 2 LED.
Screw the plastic cap back on the plug and test the monitor in the manner described. You should be able to load easily. Using a diode different from the one listed below will change the degree of brightness of both LEDs.
The case for the monitor can be constructed from thin crating wood or similiar material. Decide how big to make it (mine was 1″ by 1-1/2″). Space and drill two holes for the LEDs. Hollow out the bottom side with a pocket knife or router. In the hollow space nest the LEDs and the diode (the tops of the LEDs should protrude above the top surface of the wood after being inserted from the bottom). Notch the bottom side of the block on either end (see diagram) deep enough to allow the cable to fit snug across the block. Cut another piece of wood to the same size. Screw it on the bottom side for a completely enclosed case. Judging the brightness of the LEDs may be easier if you paint the monitor case a dark color.
The monitor is now set: It will make little difference whether the monitor plug is hooked to the recorder or to the ZX80.
A further benefit of the monitor is in searching for a program on a tape. If the monitor is plugged into the recorder, you will see both LEDs flash during voice portions of the tape (a steady bright glow indicates a program). Another benefit is that it works with the ZX81 as well as with ZX80.
Loading is Easily Done with your new monitor!