Bench-test on an off-the-shelf dev board before anyone draws a circuit.
A team wanted a small sensor device and went straight to designing a circuit board. Months later the board arrived, and the first thing they learned was that the sensor they chose did not behave the way the data sheet suggested. The board was fine. The idea needed changing.
Off-the-shelf development boards, such as an ESP32 board, cost little and come with Wi-Fi, Bluetooth, pins and plenty of examples. You can wire a sensor to one on a desk, in an afternoon, and learn if the concept works.
A custom board answers a different question: can we build many of these, reliably, at a size and cost that make sense? You only need that question answered once the first one is settled.
What to do
- Write the one question you need answered, such as: can this sensor read reliably through this housing?
- Pick a dev board and breakout parts that cover it. Wire them up on a breadboard.
- Write a few lines of test code. Log readings to a file or the serial monitor.
- Test in the real conditions: heat, vibration, wet, power from the real battery.
- Record what failed and what surprised you.
- Only when the bench test passes, start a custom board, using the working bench setup as the reference design.
When not to
If the product depends on a size, weight, regulatory testing or power budget that a dev board cannot represent, you may need a custom board earlier. Even then, bench-test the risky part separately first. And if a ready-made module already does the whole job, buy it and stop.