# homemade jbc soldering station design help / verification

#### super7800

Joined Apr 3, 2019
32
hello!

this post is going to be fairly long, so if you want to skip straight to my question/ problem, they will be underlined at the bottom. schematic below aswell

so i am designing a 4+1 JBC soldering station. 4 tools, but 1 of which is going to be the tweezers. to start out, i plan on only buying the components for 1 channel.

ill now describe how a single channel works. so on a jbc tip (see picture), there are 3 terminals. this becomes a problem when we want to read the thermocouple, so we need a zero crossing detector. in order to prevent overcurrent, i have also added a ACS712ELCTR-20A-T ic. the heater is driven by a triac. jbc went out and made it difficult to read the thermocouple by using a nonstandard design, so to read it i have implemented an op-amp circuit, similar to one found online from someone doing something similar.

here is a snipit of my schematic showing this stage, and of the jbc tip.

i also want to add sleep functionality, as i want to use the jbc stands. for this i'm using two TLP291-4, 4 channel opto isolators. two sleep lines per stand, thus i need 8 isolated channels. im a bit confused about how jbc does this with a single line, but i think i got it and came up with this: (the ground connection got cut off, as there is another unrelated component using this)

i'm using two (three?) ADS1115IDGSR‎ for current/ tempeture measurments from the op amp (the ?? lines go to the op amp)

everything mentioned thus far is entirely optically isolated from the microcontroller. might be unnescessary, but i like to keep thing seperate. the control logic is an ATMEGA2560-16AU, and the display is a 3.94" lcd touch display.

now onto why i'm posting this: my questions/ misunderstanding

a major confusion i have is how the grounds (not earth ground) are connected. looking online at designs, i'm having a hard time understanding this. in the above op- amp circuit, are the grounds connected ok?

here is the transformer layout. two 24vac 7.5a torroidals, and one wall wart. can i connect the "grounds" like this? (of the two torroidals, the wall wart is an entirely separate isolated ground) am i having a fatal misunderstanding of this design?

if anyone wants it, i could post my full schematic. the reason i'm not is that its a bit of a mess right now.

any help, recomendations, personal experience, or problems you see with my design are greatly appreciated.

thanks!

#### KeithWalker

Joined Jul 10, 2017
1,062
hello!

this post is going to be fairly long, so if you want to skip straight to my question/ problem, they will be underlined at the bottom. schematic below aswell

so i am designing a 4+1 JBC soldering station. 4 tools, but 1 of which is going to be the tweezers. to start out, i plan on only buying the components for 1 channel.

ill now describe how a single channel works. so on a jbc tip (see picture), there are 3 terminals. this becomes a problem when we want to read the thermocouple, so we need a zero crossing detector. in order to prevent overcurrent, i have also added a ACS712ELCTR-20A-T ic. the heater is driven by a triac. jbc went out and made it difficult to read the thermocouple by using a nonstandard design, so to read it i have implemented an op-amp circuit, similar to one found online from someone doing something similar.

here is a snipit of my schematic showing this stage, and of the jbc tip.
View attachment 189341View attachment 189342

i also want to add sleep functionality, as i want to use the jbc stands. for this i'm using two TLP291-4, 4 channel opto isolators. two sleep lines per stand, thus i need 8 isolated channels. im a bit confused about how jbc does this with a single line, but i think i got it and came up with this: (the ground connection got cut off, as there is another unrelated component using this)
View attachment 189343

i'm using two (three?) ADS1115IDGSR‎ for current/ tempeture measurments from the op amp (the ?? lines go to the op amp)
View attachment 189348

everything mentioned thus far is entirely optically isolated from the microcontroller. might be unnescessary, but i like to keep thing seperate. the control logic is an ATMEGA2560-16AU, and the display is a 3.94" lcd touch display.

now onto why i'm posting this: my questions/ misunderstanding

a major confusion i have is how the grounds (not earth ground) are connected. looking online at designs, i'm having a hard time understanding this. in the above op- amp circuit, are the grounds connected ok?

here is the transformer layout. two 24vac 7.5a torroidals, and one wall wart. can i connect the "grounds" like this? (of the two torroidals, the wall wart is an entirely separate isolated ground) am i having a fatal misunderstanding of this design?
View attachment 189354

if anyone wants it, i could post my full schematic. the reason i'm not is that its a bit of a mess right now.

any help, recomendations, personal experience, or problems you see with my design are greatly appreciated.

thanks!
I have designed my own soldering station and would like to help but being an "old timer", I find the modern method of presenting a circuit diagram is extremely confusing. It would take up far too much of my precious time to follow all the labels on the different lines to be able to understand what is connected to what. If you can come up with a diagram in the older style, with everything shown in one diagram with all the interconnections, I can offer my experience to help.
Regards,
Keith.

#### super7800

Joined Apr 3, 2019
32
hello and yes i agree sometimes looking at a diagram using net flags can be confusing, however i find it makes for a nicer final schematic, but does take longer to trace and understand the connections.

here is the design with all connections (excluding the two AC connections) "hardwired". please note that i am excluding the circuitry for the remaining 3+1 channels, as they are identical in design. also only the isolated mains side, not the micro-controller side, is shown. i am also excluding the aforementioned sleep circuit, as its shown above, and has to use net ports as it simply goes to a connector. also on the triac driver circuit, disregard the resistor/ capacitor value. those where calculated for a different voltage (220), and i am yet to-do the math to correct them.

my schematic editor is not wanting to export a png, so here is a low resolution screenshot followed by two higher resolution screenshots. i hope it is readable.

any advice/ problems/ recommendations you have for my design is greatly appreciated. to see my questions/ explanations, please see my first post. thanks!

#### KeithWalker

Joined Jul 10, 2017
1,062
hello and yes i agree sometimes looking at a diagram using net flags can be confusing, however i find it makes for a nicer final schematic, but does take longer to trace and understand the connections.

here is the design with all connections (excluding the two AC connections) "hardwired". please note that i am excluding the circuitry for the remaining 3+1 channels, as they are identical in design. also only the isolated mains side, not the micro-controller side, is shown. i am also excluding the aforementioned sleep circuit, as its shown above, and has to use net ports as it simply goes to a connector. also on the triac driver circuit, disregard the resistor/ capacitor value. those where calculated for a different voltage (220), and i am yet to-do the math to correct them.

my schematic editor is not wanting to export a png, so here is a low resolution screenshot followed by two higher resolution screenshots. i hope it is readable.
View attachment 189386
View attachment 189387View attachment 189388

any advice/ problems/ recommendations you have for my design is greatly appreciated. to see my questions/ explanations, please see my first post. thanks!
That really doesn't help at all. I can't read any of the small blue labels so I have no idea where the soldering iron thermocouple or where the element SCR are connected. Below is the circuit I developed. I see how easily it could be controlled with a microprocessor.

#### super7800

Joined Apr 3, 2019
32
hello!
i understand how not showing where the iron connects in detail can be confusing, so i added it to the schematic. also removed all net tags (except for +5v, -5v, & GND). i also increased the font size on the major components.

hope this is clearer. thanks!

Last edited:

#### KeithWalker

Joined Jul 10, 2017
1,062
It is clearer now. I see you are sensing the return current from the element. Are you using that to detect amplitude and phase for control? From what I see, everything looks good. The results you get will depend on the software you write to control it. Will you be using integral control for sudden thermal load changes?

#### super7800

Joined Apr 3, 2019
32
hello!

i am using the current sensor for overcurrent protection, as JBC irons vary in wattage, from the stuff for smd to the stuff for soldering massive components. i could just program it to prevent this without using a sensor, but a sensor is ~3$, and a single JBC tip is ~50$, so adding extra protection, to me at least, was a good idea.

to detect zero-crossing, i'm using a dedicated circuit (shown in schematic). since the heater and thermocouple share wires, i use the zero crossing to detect the best time to take the temperature.

i haven't thought much about the software side yet.

so my major question about my design is the grounds (not earth ground). can i connect the grounds of the ac and dc? (the micro controller is completely isolated from the drive side) also, can i connect the grounds of two separate transformers? i know on mains its a bad idea, but when isolated by transformer, i don't know. i don't do very many designs using AC.

here is a schematic showing what i mean. please note that each transformer actually drives two channels each, but for simplicity they are shown only driving one.

any help/suggestions/problems are greatly appreciated. thanks! hope my schematic is clear.

#### KeithWalker

Joined Jul 10, 2017
1,062
hello!

i am using the current sensor for overcurrent protection, as JBC irons vary in wattage, from the stuff for smd to the stuff for soldering massive components. i could just program it to prevent this without using a sensor, but a sensor is ~3$, and a single JBC tip is ~50$, so adding extra protection, to me at least, was a good idea.

to detect zero-crossing, i'm using a dedicated circuit (shown in schematic). since the heater and thermocouple share wires, i use the zero crossing to detect the best time to take the temperature.

i haven't thought much about the software side yet.

so my major question about my design is the grounds (not earth ground). can i connect the grounds of the ac and dc? (the micro controller is completely isolated from the drive side) also, can i connect the grounds of two separate transformers? i know on mains its a bad idea, but when isolated by transformer, i don't know. i don't do very many designs using AC.

here is a schematic showing what i mean. please note that each transformer actually drives two channels each, but for simplicity they are shown only driving one.

View attachment 189509

any help/suggestions/problems are greatly appreciated. thanks! hope my schematic is clear.
Yes, you can connect all of the grounds together that are shown on your circuit. Connect each circuit ground using a separate conductor right back to the transformer secondary ground. This will minimize interference between the different circuits.
It is unfrotunate that the JBC irons have the thermocouple internally connected to the ground side of the element. It means that the controlling circuitry has to be that much more complex. I am using the very inexpensive Hakko handles and elements. That is why my soldering station is so very simple. thermocouple is completely seperate from the element, and by rectifying the element supply, I can control it with a power MOSFET. It manages to maintain the tip temperature within a couple of degrees C.