Guidelines for a Better Design
- Follow some conventions in a consistent manner. For example, use
red wires for VDD and black wires for GND connections. Color-coding
the wiring on the design makes it easier to see wiring errors and
debug the design.
- Define your power rails so that a chip can access VDD and GND from
both sides. This will reduce the number of wires crossing the chip.
Put small bypass capacitors (0.1uF) between VDD and GND near the
chips to counter voltage glitches.
- Before powering up the board, check for shorts between the VDD and
GND inputs of the board using the multimeter on the bench.
- Check the power supply voltage on the board to make sure that it
is 5V. If the circuit sinks a large amount of current (especially
bipolar chips) and the chips are not fully powered up you can try
increasing the power supply voltage a little bit.
- Good floorplan on the protoboard will also help you in debugging a
design easily. Ten minutes of floorplanning will save an hour of
debugging. Messy wires and components tend to hide fatal bugs.
- Check each chip (if possible) with the Chip Tester. Try to test a
chip before adding it to the circuit. If a chip is faulty, it should
be thrown away after informing the TA or Steve.
- Try to wire "around" the chips. Wires crossing over a chip only
make it harder to remove if it is suspected of being faulty.
- Double check the final design on the protoboard before applying
power. Make sure all the chips have been wired up properly and all the
right connections have been made. Upside-down chips and/or improper
wiring (e.g. shorts) can burn the chips and ruin the lab equipment.
- Learn to set up problems in logic analyzer before asking TA for
help. TAs can only recognize signals rather than board design. Once
problems are set up, bugs are easier to identify.
- There are three ways to form a pull-up connection (high voltage on
- Using a pull-up resistance between a pin and VDD is
very expensive as you will need a lot of resistors which the lab is
unable to supply.
- You can use an inverter between the pin and a GND wire. This inverter's output can
supply a high voltage to a lot of pins simultaneously.
- You can also use another device available in the lab which
contains a few 1K or 10K resistors inside a single package with all of
them having one common port. You can ask your TA about this device.
- For debugging purposes, you can use LEDs with suitable resistors
in series for easy identification of different signals. The lab might
not have them in quantity.