Good Resources Battery University Lithium Cell Voltage 3.0 to 4.2V (cell voltage typically specified as 3.7V) Series battery packs: 2 cells in series: 6.0 to 8.4V (7.4V typ) 3 cells in series: 9.0 to 12.6V (11.1V typ) 4 cells in series: 12.0 to 16.8V (14.8V typ) Don’t allow the battery voltage to drop below 3.0V […]
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NiMh Batteries
NiMh Cell Voltage 0.9 to 1.5V (cell voltage typically specified as 1.2V nominal) General Notes High self-discharge rate of over 30% per month in common nickel metal hydride batteries There tends to be 2 grades of battery:- consumer where capacity may be higher but number of discharge cycles will be lower (big numbers are best), […]
I2C Bus Interfacing
Interfacing 5V and 3V3 I2C busses You can't connect a 5V I2C bus (e.g. an Arduino board) to a 3V3 I2C device (e.g. a Raspberry Pi) without damaging it, so in this situation you would need to its the 3.3V I2C bus to connect to a 5V I2C device. This means no over voltage damage […]
I2C Bus General
I2C Clock Speed 400kHz means the clock speed for a complete high low clock sequence. So 2.5uS per cycle, 1.25uS per high or low clock edge. Pull Up Resistors Minimum current that all devices must be able to sink = 3mA This sets the lower resistance limit on the pull-up resistor. 1K7 for a 5V system […]
Bandwidth vs Sample Rate
Bandwidth vs Sample Rate Bandwidth is not how many measurements are taken per second, that is the sample rate and they are different! Bandwidth is maximum frequency of an input signal which can pass through the analog front end of the scope with minimal amplitude loss (from the tip of the probe to the input of the […]
Disc Drive 4 pin Power Connector
Typically used for pre SATA hard disk drives. AMP EI Series part numbers: AMP / TE Connectivity 1-480424-0 and 163304-2 – Cable socket AMP / TE Connectivity 350211-1 – Vertical PCB header AMP / TE Connectivity 174804-1 – Right Angle PCB header Pin Name Color 1 +12VDC Yellow 2 Ground Black 3 Ground Black 4 +5VDC Red
PCB Stackup
Asymmetric Layer Stackup It is best to keep a boards layer stackup symmetric to prevent board warpage. Some manufacturers may be willing to go to the extra effort to fight the warpage from an asymmetric stackup (often by them having to make multiple attempts to get it right for your stackup) but at cost and risk. […]
Ethernet Cabling
Cat5 – Up to 100Mbps Cat5e – Up to 1000Mbps / 1Gbps Cat6 – Up to 10Gbps
Balanced Audio Connections
Creating A Balanced Line Output From an unbalanced line level signal Converting Balanced Line Level to Un-Balanced NOTE: The 22K resistors used here work great, but 22K can cause noise to be picked up from close digital tracks (e.g. 3.3V clock signals). We discovered just such a problem on a digital PCB causing pickup to occur […]
Standards For Power Supplies
EN 61000-3-2 – Limits for Harmonic Current Emissions See which class your product needs its power supoply to comply with here. Lighting equipment – EN 61000-3-2 Class C complaince requried General equipment – EN 61000-3-2 Class A complaince requried