Implementing Ship Mode to Your Product

As global manufacturing and distribution increases, many original equipment manufacturers always look for creative ways to extend battery life during shipping and shelf life at big-box warehouses. Keeping the battery sufficiently charged during shipment enables a consistent out-of-box experience for the end-user. A solution that has gained popularity is using a ship mode feature that keeps devices in a low-power state during shipment and while on the shelf. Here is my solution using a load switch from TI, TPS22915B.

This is how the circuit works. Before the button is pressed, the solution is in ship mode, meaning that the system is not powered and the TPS22915 B load switch is turned off. When the button is pressed, the voltage from the battery is passed through the PMOS to the ON pin of the TPS22915B. The voltage enables the TPS22915B, brings VOUT high, turns off the PMOS, and powers the system. The ON-pin is pulled up to VOUT, which makes keeping the load switch enabling even after the button is released.

Making your own PCB by Etching method

1) Artwork Printing: 

Print your artwork on a transparent sheet.

2) Exposing:

Kinsten Presensitized PCB is used for this prototype as it is low-cost and easy to work. Remove the light-proof protective film and expose the board in the Kinsten UV exposure box for 90 seconds.
Align the artwork with the PCB inside the vacuum clamp, and leave it inside the exposure box for about 5 minutes.

3) Developing:

A sachet of DP-50 developer is mixed with 1 liter of 25°C water in a plastic container. The exposed PCB is gently agitated in solution. The exposed areas of resist will dissolve into the solution, leaving the green resist in areas that were not exposed to UV light as below.

4) Etching:

Etching copper is done in the Kinsten Etching Tank for 4 to 10 minutes. Pour enough etching solution (Ferric Chloride or Ammonium Persulphate) into the tank and immerse the board. Use the air pump to allow the etchant to be bubble agitated until the unwanted copper foil is etched away, only the circuit patterns are left. Rinse the board with plenty of water.

Remember “Safety First” always wear rubber gloves and protective eyewear when working with this etching compound. Once you've etched your board, the leftover solution should not pour down the drain (legally). Take it to a hazardous waste facility.

Here is the final outcome. For better results, make PCB trace thickness at least 10 or 12 mils and leave a wider gap between trace and GND copper pour.

Estimating Product life Span

To predict the lifetime of a product, manufacturers usually conduct accelerated temperature & Humidity tests. We usually conduct the accelerated test under conditions that are much more severe than the actual operating conditions and record test hours, and time-to-failure. Then we estimate/ calculate the product lifespan using Peck's Power Law.

In the below example, the estimated lifetime of the product under test is 12 months if it survives for 96 hours at 80 °C with 90% RH. Assuming the product's normal upper operating limit of 40 °C and 50% RH, we have got acceleration factor of 92.48.

Digital filtering technique , ADC Filter

A digital filter system usually consists of an analog-to-digital converter (ADC) to sample the input signal, followed by a microprocessor and some peripheral components such as memory to store data and coefficients of the filter, etc.

Program Instructions (software) running on the microprocessor implement the digital filter by performing the necessary mathematical operations on the numbers received from the ADC.

Here is a simple digital filter that identifies and rejects transient response signals. It returns the average of the best two samples of the last three. The third sample is discarded.

Algorithm:

1. Calculate the average of the last 3 samples

2. Identity the sample furthest from the mean value (which is the outlier)

3. Discard the outlier and average the remaining two samples

4. Returns float value of the averaged data (y(i)).

EEVblog uCurrent - Precision nA Current Measurement Assistant

Here is another useful circuit from EEVblog, that can be used to measure from pico amps to amps current.