#Eetech smart timer user manual mod#
#Eetech smart timer user manual manual#
#Eetech smart timer user manual series#

If you're not in America, you may find Digikey's shipping charges are a bit crazy, and you may want to look at Farnell (now Element 14 I think) or RS Components, or some other supplier. I would like to hear what other forum members think of this matter. This circuit relies on the fusible input resistor to absorb the energy from any mains spikes. The standard arrangement, using 1N400x diodes and a separate zener with an electrolytic across it, would be harder to damage because the 1N400x diodes can handle large brief spikes and the electrolytic would help to protect the zener. I'm not sure whether using small diodes in the bridge is a good idea they could be susceptible to damage from spikes on the mains. R4 could be replaced by a 1M trimpot if desired. This will vary somewhat depending on the Vgs threshold of Q1. The delay is set by C3 and R4 and is about 23 seconds. This design doesn't have explicit positive feedback, but still has this behaviour, because as soon as current starts to flow in the relay coil, the positive rail voltage starts to drop, and this is coupled through the timing capacitor back to the input of the voltage detector (Q1), reinforcing the change from OFF to ON. It avoids the separate zener and therefore saves space.Ī circuit like this would normally include Schmitt trigger behaviour, so that there would be a clean, well-defined change from the OFF state to the ON state. This clever idea actually comes from your PIR circuit I didn't think of it myself. This provides full-wave rectification and simultaneously clamps the positive rail to the zener voltage. The input bridge rectifier uses two normal diodes and two zener diodes. There are a few features of this design that may interest other Electronics Point users. If you want to build it, let me know, and I will post a list of links to appropriate components on the Digikey site. (This assumes that the alarm circuit is normally open for security reasons, sometimes normally closed circuits are used for alarm signals.)Īll of the components in this design are available from Digikey.

#Eetech smart timer user manual series#

In your application, this circuit would be connected directly to the mains supply and the contact of this relay coil would be wired in series with the contact from the PIR device. The relay must have a 24V DC coil with a resistance of about 1600 ohms (i.e. This relay will close after about 20 seconds after power is applied to the circuit. The resistor named RELAY_COIL at the right side represents the coil of a relay. It must be enclosed and insulated so that no part of the circuit can make contact with any conductive component, especially anything that could be touched by a person. This circuit is powered directly from the mains, and should all be considered LIVE. Or as Duke suggested, you could use a normal time delay relay, if you can tolerate a delay in the alarm activating on a genuine alarm condition.Įdit: I can probably simplify the circuit down to one resistor, one electrolytic capacitor, one transistor, and two diodes.

I doubt there's an off-the-shelf solution, but you could Google words like power delay relay. I'm sorry that a hack isn't as straightforward as I expected.Īn external delay box is totally possible but would probably be more work to build than a hack. That's a long way away, and you would need to pay for postage both ways.

#Eetech smart timer user manual manual#

If you can link to a user manual for the PIR unit, I may be able to understand what the LDR does, and be able to say more definitely whether a modification will work.Īlternatively, if you can spare it for a week or two, you could send it to me here in New Zealand. Would there be room to fit that many components in the enclosure? You would need to make the circuit up on a small piece of stripboard, cut one track on the main board, and connect the stripboard to the main board with three wires. I can draw up a modification that MAY work, and you could try it - it would involve five resistors, two small MOSFETs, one diode and one electrolytic capacitor.

#Eetech smart timer user manual mod#

To be sure that the mod would work properly, I would have to reverse-engineer the whole circuit. So, intercepting the control signal to the relay coil might affect the rest of the circuitry.

It seems to connect to the LDR (light-dependent resistor - marked CDS on the board) and the trimpot nearby. The problem is that the output that drives the relay also feeds some other circuitry. The main supply rail is +24V (the relay has a 24V coil). The relay is driven directly from one of its outputs, on pin 14. The LM324 is a very common IC, as you've probably discovered. The circuit and the PCB seem to be very well designed.