Tape Recording

To avoid future aggravation, it is worth investing in a few hours to find the best settings for your tape recorder controls, and possibly the brand of tape used, so you can be confident of being able to retrieve whatever valuable information you commit to tape.

The simplest test is that given in chapter 1 of Atomic Theory and Practice', and this should be used first. For a more stringent test, we need to record and retrieve data in blocks, as the Atom normally does. This can easily be done by saving the contents of the 4K BASIC ROM;

*SAVE "TEST TAPE" C000 D000

which gives a tape lasting about 4 minutes. A catalogue of the tape should then show 16 consecutive blocks, as below, if the Atom can successfully read the block headers.

TEST TAPE	C000 C000 0000 FF
TEST TAPE	C100 C000 0001 FF
TEST TAPE	C200 C000 0002 FF
TEST TAPE	C300 C000 0003 FF
TEST TAPE	C400 C000 0004 FF
TEST TAPE	C500 C000 0005 FF
TEST TAPE	C600 C000 0006 FF
TEST TAPE	C700 C000 0007 FF
TEST TAPE	C800 C000 0008 FF
TEST TAPE	C900 C000 0009 FF
TEST TAPE	CA00 C000 000A FF
TEST TAPE	CB00 C000 000B FF
TEST TAPE	CC00 C000 000C FF
TEST TAPE	CD00 C000 000D FF
TEST TAPE	CE00 C000 000E FF
TEST TAPE	CF00 C000 000F FF

If all is well, we can then check the Atom can read all the tape, including the actual data, by;

*LOAD "TEST TAPE"

This makes the Atom try to read data from the tape and write it to the BASIC Read Only Memory, which is of course impossible, but the Atom will check that the data there matches the data it tried to write. If the data are read without error, the cursor will re-appear about four minutes later.

Problems and Cures

If you cannot save and load programs despite careful adjustment of the recorder's level and tone controls, then;

• Try removing the CAS IN' connections from the recorder when saving,
  and removing the 'CAS OUT' connections when playing back.
  Some cheap recorders don't like simultaneous connection of their input and output sockets.
• If you'd been running the recorder from the mains,
  try using batteries to eliminate the chance of ground loops introducing mains hum onto the signal.
• If you'd been running the recorder from batteries, make sure they are fresh.
  A fast rewind can temporarily deplete the batteries,
  so try resting them for a minute before recording or playback.
• Ensure the tape head is well past the tape header, and allow a few seconds for the recorder to pick up speed before starting to record.
• Ensure the tape head is clean.
• Try different types of tape. 'High energy, low noise' type are usually best.
• Ensure the plug connections are firm and that they and the
  level and tone controls aren't causing any 'crackling' noises.
• The recorder should be at least a metre away from your TV,
  monitor or any other potential source of radiated interference.
• Listen to the signal, especially the periods of 2400Hz tone.
  It should be free of pops, crackles or excessive wow or flutter.

As supplied, the recorder interface of the Atom is optimised for use with the 'Aux' or Amp' recorder sockets which expect a signal level of around 300 to 500 mV at an impedance of 1 to 10k. If you are feeding into the 'Mic' socket, then the level expected is usually 5 mV, and the resulting overload can have some very odd effects, especially if the recorder has automatic level control.

In this case, the Atom's 'CAS OUT' level should be reduced drastically; either by increasing R29 to between 100k and 1M, or by adding an external voltage divider as Fig. 1. The latter is preferable as it avoids tampering with the Atom's PCB, and can easily be changed for different recorders by fitting miniature resistors in the recorder connectors.

If the recorder output level is not enough to drive the Atom's interface properly when reading tapes, then the gain of the input amplifier IC46 can be increased by increasing R34 to 100k or 200k. Alternatively, a 3k3 to 10k resistor can be added in parallel with R37. Some cheap cassette recorders produce a lot of high-frequency noise on playback. This may not be noticed if the loudspeaker has a poor high-frequency response, but can upset the Atom. If you think this may be the problem, a simple low-pass filter (Fig. 2) may help.