Opto-isolators

An opto-isolator is a component that transfers electrical signals between two isolated circuits by using light. This allows transmission of electrical signals between systems of different voltages with complete electrical isolation up to the rated isolation voltage. A 5 V logic signal, for example, might switch a mains circuit using an opto-isolator without risk of the mains … Continue reading "Opto-isolators – intro"

You can fabricate an opto-isolator using components from the scrap bin. This may be useful in special circumstances or when you need an opto-isolator in a hurry but don’t have one to hand. All transistors exhibit the photo-transistor effect and are packaged in opaque material to prevent stray light interfering with their operation in circuit. It … Continue reading "DIY opto-isolator"

LDR Summary LDRs are light dependent resistors. Resistance decreases with increasing light levels. Typically > 1 MΩ when dark and < 1 kΩ in high light levels. Response time of 2 – 50 ms. (Much slower than photo-transistors.) They have a “light history”. Characteristics change a little as they acclimatise after long periods in darkness. LDRs are more … Continue reading "Light dependent resistor (LDR)"

Opto-triacs summary Opto-triacs or solid-state relays (SSR) consist of an infra-red LED and a triac in one package. The LED is switched on and off by a low-power DC control circuit and this switches the triac which can be used to control AC devices up to mains voltages. Opto-triacs provide electrical isolation between the control circuit … Continue reading "Opto-triacs, solid-state relays (SSR), zero-cross and how they work"