- Joined
- Jan 21, 2010
- Messages
- 25,510
There is pretty much no chance a power transistor is going to work in the place of Q1 and Q2. I would recommend the device specified.
Let me do some quick calculations for you...
At 50mA collector current the transistors have a guaranteed gain of 50, so given the 15k(ish) resistance in series with the base, you would not expect the transistor to be able to drive a relay that required much more than 30mA.
What current does the relay draw? if it's more than 30mA, it aint gonna work. (well it might, but not reliably) In this case, replacing it with a mosfet is probably a good idea. A darlington pair (even of 2N3904's) would help.
What is the resistance of your LDRs in bright light and darkness?
If the voltage at pin 8 of IC1c falls below 1V at the twilight point (when you want it to return home) then you're not going to be able to adjust VR2 to make it work at that point. This just means it will return home earlier in the day.
As I suggested, change VR1 so that the wiper is disconnected from ground, and connected to the top of C1 and R2 in lieu of them being connected to the top of VR1. Increasing R1 to 4k7 is probably not a bad thing.
For testing, replace the coil(s) of the relays with a LED and a (say) 1k resistor. That will show you when the relay is supposed to pull in.
Make sure that VR2 is adjusted all the way to ground and that LED1 is extinguished when you're testing the operation of the rest of the circuit. LED2 will have to be illuminated for perhaps 2 minutes or so before the relay pulls in. If LED2 extinguishes even for an instant before that time, you start from scratch again. Perhaps you're not expecting this sort of time delay.
Try to keep your answers separate from the quoted text (and only quote what you have to) and you'll have fewer problems with the software requiring that you type 10 more characters...
Let me do some quick calculations for you...
At 50mA collector current the transistors have a guaranteed gain of 50, so given the 15k(ish) resistance in series with the base, you would not expect the transistor to be able to drive a relay that required much more than 30mA.
What current does the relay draw? if it's more than 30mA, it aint gonna work. (well it might, but not reliably) In this case, replacing it with a mosfet is probably a good idea. A darlington pair (even of 2N3904's) would help.
What is the resistance of your LDRs in bright light and darkness?
If the voltage at pin 8 of IC1c falls below 1V at the twilight point (when you want it to return home) then you're not going to be able to adjust VR2 to make it work at that point. This just means it will return home earlier in the day.
As I suggested, change VR1 so that the wiper is disconnected from ground, and connected to the top of C1 and R2 in lieu of them being connected to the top of VR1. Increasing R1 to 4k7 is probably not a bad thing.
For testing, replace the coil(s) of the relays with a LED and a (say) 1k resistor. That will show you when the relay is supposed to pull in.
Make sure that VR2 is adjusted all the way to ground and that LED1 is extinguished when you're testing the operation of the rest of the circuit. LED2 will have to be illuminated for perhaps 2 minutes or so before the relay pulls in. If LED2 extinguishes even for an instant before that time, you start from scratch again. Perhaps you're not expecting this sort of time delay.
Try to keep your answers separate from the quoted text (and only quote what you have to) and you'll have fewer problems with the software requiring that you type 10 more characters...