Electronics > Projects, Designs, and Technical Stuff
Need some help with a 555 timer circuit
Ian.M:
OTOH, some flavor of 555 chip is likely to be obtainable for the rest of this century, and you can buy them retail even in 3rd world s--tholes.
Fixed that for you:
--- Quote from: Pizzashape23 on August 13, 2020, 12:39:40 pm ---In all seriousness though, if you had to pick between either 555 circuit in this topic which would it be? I think i have learned more than enough and don't really feel like opening another can of worms, as interesting as it seems.
--- End quote ---
Its easier to make my version general purpose as it really doesn't care if the input is from a switch or is a 'logic' signal on a wire from something else, but if you can guarantee a real switch with short wiring, eblc1388/Zero999's version is plenty good enough. Add a RC network on its Reset pin to prevent it firing on power-up glitches and, to save parts, use its output to drive a MOSFET via a small gate resistor. If you use a beefy enough MOSFET and a small enough gate resistor, you could probably drive the solenoid directly!
Pizzashape23:
In that case I will probably end up using your design.
The final build will not have short switch wiring (I can't have the circuit too close to the furnace), I am still unsure about what switch i'm going to use and I like the idea of being able to reuse the design and pcb for other projects. (Especially when buying bulk parts/pcbs is generally cheaper)
I like where you are going with integrating mosfet control into this board but unfortunately thats a no go, part of the idea behind using relays and cutting all the power was to give me the option to easily increase the amount of solenoids in the system. (There are curently 3) It would also remove the sensor from the original circuit. (It would only trigger the solenoid when a rod was correctly seated).
The final system should theoretically allow the solenoid to trigger for a set period of time on button press, as long as the sensor is detecting a rod.
P.S I ended up using a ground plane, I decided to not extend it to under the relays, would this be an issue?
P.P.S Should I post a final circuit and PCB design?
Ian.M:
*DO* post your PCB layout and final schematic - peer review is almost always useful.
I wouldn't put a ground plane under relays switching power circuits. Others may have different opinions.
Pizzashape23:
I just wanted to thank everyone who contributed to my final design, all your help has been greatly appreciated.
Attached are my final schematic (Doesn't include connectors, Indicator Led or 24v to 12v convertor), my pcb and the ground plane to make the slots where traces need to cross easier to see.
I have ordered the necessary components to bread board the circuit before printing the pcb, so until then any and all feedback in regards to optimizastion, design, design checking, layout, etc is helpful.
If I remember I will make sure to come back and post an image of the assembled pcb.
Zero999:
--- Quote from: Pizzashape23 on August 18, 2020, 12:29:21 am ---I just wanted to thank everyone who contributed to my final design, all your help has been greatly appreciated.
Attached are my final schematic (Doesn't include connectors, Indicator Led or 24v to 12v convertor), my pcb and the ground plane to make the slots where traces need to cross easier to see.
I have ordered the necessary components to bread board the circuit before printing the pcb, so until then any and all feedback in regards to optimizastion, design, design checking, layout, etc is helpful.
If I remember I will make sure to come back and post an image of the assembled pcb.
--- End quote ---
That looks good to me. The decoupling capacitors are near the supply pins to the ICs, which is great.
Is there any reason why you're not using the NE556 or better still the CMOS TS556/ICM7556? The 556 means it has two 555 timers in the same package, which saves space and makes one of the 10µF capacitors unnecessary. The CMOS versions (TS/ICM7) use much less power and don't draw such big power spikes, when the output changes state, so can use much smaller 100nF decoupling capacitors.
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