Fast opto isolators (like the ACSL6400, HCPL-263L, etc) have a max propagation delay specification of around 100nS. To pass say a UART signal through, it is easy to calculate the affect of the propagation delay on the signals. Actually for a single direction signal like a UART the propagation delay isn't too much of an issue at all if it is reasonably constant for […]
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Custom Plastic Enclosures
No tooling required plastic enclosure manufacturers Smartbox offer a very viable alternative to machined off the shelf plastic enclosures. These guys will bend and machine sheet plastic to make fully customized enclosures without the need for any plastic moulds etc. Using different plastic materials and shaped edges you can end up with a really attractive […]
Connector Crimp Tools
We'd not use these in a production environment ourselves as manufacturers own crimp tools are the only way to ensure reliabiliy. However when faced with needing to make up some new crimp based connector for development and being faced with the manufacturers own tool costing a small fortune, these bad boys from ebay can come […]
Logic Analysers & USB Analysers/Scopes
We used the original DigiView from Tech Tools and liked it a lot but eventually found their software too lacking in comms decoding and search features so we changed to a USBee AX. This is a pretty good logic analyser with a single channel scope also built in, but it relies on the USB connection into the PC […]
Potential Dividers
Calculating any value for a potential divider Vin > R1 > Vout > R2 > 0V Vin = Vout * (R1 + R2) / R2 R1 = (Vin * R2 / Vout) – R2 R2 = Vout * R1 / (Vin – Vout) […]
RMS Voltage of an AC Waveform
"RMS" stands for "Root-Mean-Squared". It is often defined as the amount of AC power that produces the same heating effect as an equivalent DC power. RMS is only relevant to varying voltages and is not used for DC analysis. For example in the UK the typical RMS mains voltage is 240V (well it used to be before […]
Spark Gaps
You can use PCB traces to create a poor mans spark gap on a PCB really easily. Whilst not as good as a proper device such as a gas discharge tube, they cost nothing as long as you have the PCB space available. Using a 8 thou / 0.2mm gap will create a spark gap that […]
DHCP Relay Agents
DHCP messages are generally broadcast, which means they are non routable (gateways won't pass them). A DHCP client and server therefore need to be on the same subnet. This restrictions would require that individual subnets each have their own DHCP server which is not practical in large networks. This problem is solved through the use of DHCP […]
LED Thermal Management
How Much Heat Is Created LEDs are not 100% efficient. Much of the power running through an LED is output as heat and needs to be dissipated. Good high power LED's, such as some Cree XLamp LEDs are over 40 or 50% efficient – that is, under normal operating conditions, approximately 50% to 60% of the input power is […]
Heat Sink Temperatures
Heatsink or metal plate temperatures These are not scientific, just us noting our experiences as its sometimes useful to know when users will be in contact with heatsink metalwork. 38ºC feels very warm to the touch but is OK to be touching for a period of time.. 42ºC feels very warm to the touch. Its not […]