Repeat customers may have noticed that we had a substantial upgrade to the website. Everything has been changed and upgraded.
We have had some issues with international customers not being able to order some ESP32 boards. The issue is fixed and everything in stock should be available to all countries that we ship to.
The shop resides at ezsbc.shop.
The price of LiPo cells available in the US marketplace is absurd. I suspect its mostly due to the difficulty in importing cells in volume from China because of the restrictions in shipping more than a small number of cells. We now stock three commonly used sizes with connectors and safety circuits installed. The capacity of the cells are 400mAh, 1000mAh and 2000mAh and they can be ordered from the store. Orders for 1 or 2 cells ship normally. More than 2 cells require ground shipping because of the restrictions on shipping cells through the mail.
The capacities quoted are measured capacities and not stated capacities by the manufacturer. The capacities are measured using the charging circuit on the boards that we cell and is typically 20% lower than the manufacturers’ stated capacity.
The capacity of a LiPo cell depends on the exact cutoff voltage for charging and discharging. The discharge cutoff voltage has a small effect on the cell capacity but the charge profile and charge cutoff voltage can have a large effect on the total cell capacity. I measure the cell capacity by charging the cell plugged into an ESP32-Bat circuit and once it is fully charged I discharge the cell with a constant current using an electronic load. I set the cutoff voltage at a point where the 3.3V LDOs enter dropout.
The PSU5 as an LM323K replacement as been in production continuously since June 2014 and thousands are in the field. Some time ago I was blindsided by an unexpected discontinuation of the switcher IC and I had to redesign the module and the Revision 2 module was introduced. There have been a few other revisions to improve the potentiometer and the calibration range.
Since the earliest units some Pinball machine users have reported a loud sound through the speakers as the machine is turned off. It is not a universal issue and I have never spent much time trying to resolve it. I have known about the issue and its cause for a long time but it was hard to fit a solution on the limited size of the module.
The noise in the Pinball machines is caused by at least two causes conspiring to make life difficult. Most linear power supplies have a mains transformer followed by a rectifier and a large electrolytic capacitor. Capacitors exhibit a phenomenon called dielectric absorption which is the name given to the effect by which a capacitor, that has been charged for a some time, discharges only incompletely when discharged. When the discharge current is removed the capacitor voltage increases with time as more of the stored charge becomes available to supply a discharge current. More information is available on Wikipedia. Electrolytic capacitors are some of the worst capacitors for dielectric absorption. This is the first cause and the second is the behavior of the PSU5 itself when the output load is small and the input voltage is close to the dropout voltage of the module. The difference between the voltage where the module turns off and where it turns on is small, only a few hundred milliVolt.
The photo above shows the behavior of the PSU5 without a load when the input power is removed. The input to the PSU5 is a 12V supply with a 47,000uF electrolytic capacitor on the input terminals of the PSU5. The yellow trace is the 5V output and the blue trace is the 12V input. The oscillation of the output voltage is definitely not desirable but in practice this is not the cause of the audio noise in the pinball machines. When the pinball machine is powered off the load does not disappear abruptly. As long as the 5V is present there will be some load on the output of the PSU5.
In the image above the load is still present and the 12V drops rapidly and the output spikes up as the input voltage recovers due to dielectric absorption. This rapid rise and fall of the 5V output will definitely cause noise on the audio output.
In the scope shot above the PSU5 turns on and off as the input is rising. This is unlikely to happen in a normal application because the rise time of the 12V is normally much faster than the rise time of the bench power supply. The output of the PSU5 starts drooping before it abruptly turns off.
The new and improved PSU5 has circuitry to prevent this behavior and it is being tested in real pinball machines to verify that it prevents the noise during turn-off.
The scope shot above shows the completely clean turn-off behavior of the PSU5_NN. The 5V abruptly turns off when the 12V reaches the dropout voltage and stays off even as the 12V rail slowly discharges. The new revision will be for sale as soon as I can confirm that it solve the noise issue.
The PSU5_NN is essentially the same as the PSU5_Rev2 except for the behavior of the trimpot. On the PSU5_NN turning the trimmer clockwise increases the voltage and on the Rev2 it decreased the output voltage. Production versions of the PSU5_NN is yellow in color. (Not yet available, ETA 12 Dec ).
After fighting with the shipping calculator we now have new shipping rates for USPS First Class mail. The shipping calculator refuses to offer First Class mail as an option so we added a table based shipping cost calculator that should fix this issue. For people in the UK, the shipping calculator would routinely produce $50 as a shipping charge and this is ridiculous since our most expensive item is only $59-95. We now offer world wide shipping for $6-95.
I hope the new shipping rates make shopping a pleasurable experience.
We are always looking for new products that solve real problems and are easy to use and master. We are almost done transferring the manufacturing of our existing products to the new equipment. This is a big task because all the pick and place programs were re-written on an unfamiliar machine. At the same time we built stock so we can spend time on the machine programming the production of new designs without having to stop midway and build some board because stock is running low.
The first time you build a board on a new machine there is a lot of setting up to do. You have to transfer the CAD data to the machine so you know where to place the parts. Then you have to mount the reel containing a part on the feeder, tell the machine that the feeder exists and where it can find the part. This goes quickly for one or two new parts but it gets tedious to do it for every part used in all the designs. You also have to figure out how the tape goes into the feeder, where the cover tape goes etc. Once you know, the next time is easier and by the filth one, it is easy. Then you end up learning how the matrix trays work and the optical alignment. Everything takes a lot of time the first time round. One of the strange behaviors of this machine is how it picks up parts from the matrix trays. It starts from the last position and ‘advances’ to the first position. My first tray was partially used so I carefully moved the parts to the start of the tray just to discover that the machine starts from the side that I had just emptied out. So I moved all fifty parts back to the other end of the tray. What a waste of time. Now, after having built panels of everything we sell we can move on to new designs.
The first new design is a small switch mode voltage regulator to fit the footprint of a standard TO-220 LM7805 type linear regulator. When the supply voltage is a little high and the load current more than a few milliamps then the linear regulators run very hot with small heatsinks. There are switching regulators of this type on the market but the suffer from two problems: Most need external capacitors and are very expensive, around $10 each. The new design has all the capacitors on board so you can remove and overheating linear regulator and drop this one in its place without having to find a place to hide a few external capacitors. The price is going to be less than $6 in singles.
Watch this space.