Electronics

Sparkle Eliminating Diode

| steelcityelectronics

Whilst flicking through an old user manual for a Toshiba Tosdic 215D single loop controller I found this gem.

sparkle eliminating diode
Don’t forget to use a sparkle eliminating diode

The user manual suggests that when interfacing inductive loads to the Tosdic 215D’s digital outputs, the user must implement sparkle eliminating diodes.

My Japanese language skills are relatively poor so I’m not sure if sparkle eliminating diode is a literal translation or a mistake from the original Japanese user manual.

Personally I like sparkle eliminating diode as it is visually descriptive. A much better explanation than the traditional freewheeling or flyback diode.

Motorola MC68705 Microprocessor

| steelcityelectronics

After clearing out an old cupboard at work, I stumbled across a couple of old Motorola MC68705P3S microprocessors. What immediately caught my attention with these chips compared to others, was that they had a ceramic package which is not very common. Additionally, they have a glass window over the chip’s die (more details on the reason for this later) allowing you to peer deep inside the chip.

Motorola MC68705P3S 28pin CDIP
Motorola MC68705P3S 28pin CDIP

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Changing HTU21D Temperature and Humidity Resolution

| steelcityelectronics

By default the HTU21D sets the temperature and humidity sensor resolutions are set at their highest. These default values are, humidity = 12bit and temperature = 14bit. This is all well and good for most situations when you are trying to get the best performance from your device. However, a higher resolution comes at the expense of increased measuring time. Consequently, a longer measuring time will increase the current consumption too.

To demonstrate, I’ve tabulated the maximum measuring times for the different sensor resolution modes from the HTU21D_datasheet.

Resolution Humidity Temperature
14bit NA 50ms
13bit NA 25ms
12bit 16ms 13ms
11bit 8ms 7ms
10bit 5ms NA
08bit 3ms NA

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Dew Point Calculation with HTU21D Humidity Sensor

| steelcityelectronics

Having both temperature and humidity sensor capabilities in a single package makes the HTU21D an ideal sensor for a home weather station. As such, if you’re a person who is interested in knowing the current weather conditions, you’ll probably want to know what the Dew Point is too. But before we can get carried away, we need to learn how to use an additional library.

Dew Point calculated with HTU21D sensor

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HTU21D Temperature and Humidity Sensor Tutorial Part 2

| steelcityelectronics

If you’ve missed out on part 1 of this tutorial, you can catch up here.

If you closely read the HTU21D_datasheet, you’ll realise that the humidity data that you read directly from the HTU21D sensor does not meet the device’s guaranteed humidity accuracy of +-3%. Additionally, the sensor is only optimised to perform in the range of 5-95%RH, the rated accuracy of +-3% only applies between 20-80%RH.

This excerpt from the datasheet shows the device’s range of performance.

HTU21D_Temperature_Compensation

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