Hi all,
First up, my apologies for another 555 thread as I can't find a similar thread to tag onto...
I'm attempting to make up a 555 circuit that will trigger a key press on a keyboard with the help of a solid state relay. I've attached a schematic of the actual 555 circuit below but without a few modifications that I'll mention later.
Essentially, I'm taking a keyboard PCB and attaching the corresponding contacts for the space bar to a solid state relay. I'm planning on having 2 relays in series - one will trigger and simulate the space bar being pressed, one relay will light up an LED and the other will simply just close an external circuit for external expansion ( one of these relays are a dual SPST relay hence 2 relays!)
So far, after about 2 days trawling through both Google here for inspiration I've come up with the circuit below but with a few modifications. For R1 I've decided to use a variable resistor (finding a 19.96KR resistor I discovered was impossible!!) which will be set and then left alone, and R2 I'm hoping to use a 432KR resistor and a 1MR Potentiometer in series so I can vary the time delay (currently from approx 3s upto approx 10s - this delay is not critical!!)
I've lost track of what I've read where but I did read something about having a capacitor as a supply bypass due to spikes from the 555 when it changes state. I read from the datasheet of the LMC555CN, that I'm hoping to use, that as it's a CMOS chip, these spikes are reduced - but the datasheet doesn't go into any further detail. As the power is being tapped off the USB port in parallel to the keyboard am I guessing correctly that it would be a good idea to include this bypass and, if so, what capacitor should I use? Also, which type of capacitors should I be using for my project - tantalums, ceramic or electrolytic as I am a complete novice!
From the LMC555CN datasheet I've noticed that the voltage output when it's in it's 'off' state is around 0.3V to 0.6V whereas the SSR's stated LED minimum forward voltage is 1.15V so am I correct is saying that when the 555 output goes low the SSR will in fact turn off? Or will there be something I need to add such as a resistor to ensure the SSR does turn off?
I'm hoping I've included enough info here but if I've omitted anything let me know!!! Also, if there is an easier way to accomplish the same task please let me know I'm all ears!!!
Many thanks!!!
First up, my apologies for another 555 thread as I can't find a similar thread to tag onto...
I'm attempting to make up a 555 circuit that will trigger a key press on a keyboard with the help of a solid state relay. I've attached a schematic of the actual 555 circuit below but without a few modifications that I'll mention later.
Essentially, I'm taking a keyboard PCB and attaching the corresponding contacts for the space bar to a solid state relay. I'm planning on having 2 relays in series - one will trigger and simulate the space bar being pressed, one relay will light up an LED and the other will simply just close an external circuit for external expansion ( one of these relays are a dual SPST relay hence 2 relays!)
So far, after about 2 days trawling through both Google here for inspiration I've come up with the circuit below but with a few modifications. For R1 I've decided to use a variable resistor (finding a 19.96KR resistor I discovered was impossible!!) which will be set and then left alone, and R2 I'm hoping to use a 432KR resistor and a 1MR Potentiometer in series so I can vary the time delay (currently from approx 3s upto approx 10s - this delay is not critical!!)
I've lost track of what I've read where but I did read something about having a capacitor as a supply bypass due to spikes from the 555 when it changes state. I read from the datasheet of the LMC555CN, that I'm hoping to use, that as it's a CMOS chip, these spikes are reduced - but the datasheet doesn't go into any further detail. As the power is being tapped off the USB port in parallel to the keyboard am I guessing correctly that it would be a good idea to include this bypass and, if so, what capacitor should I use? Also, which type of capacitors should I be using for my project - tantalums, ceramic or electrolytic as I am a complete novice!
From the LMC555CN datasheet I've noticed that the voltage output when it's in it's 'off' state is around 0.3V to 0.6V whereas the SSR's stated LED minimum forward voltage is 1.15V so am I correct is saying that when the 555 output goes low the SSR will in fact turn off? Or will there be something I need to add such as a resistor to ensure the SSR does turn off?
I'm hoping I've included enough info here but if I've omitted anything let me know!!! Also, if there is an easier way to accomplish the same task please let me know I'm all ears!!!
Many thanks!!!
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