JBC-mini - a low cost T245 handle controller - Page 1
Forum section: electronics / projects

author: poorchava
author_rank: Super Contributor
timestamp: May 28, 2014, 01:56:17 pm
content: I want a JBC soldering station. I've wanted one since I had a chance to use it at work. Unfortunately in EU they are expensive as hell, and even more so when you live in eastern europe - the most basic station is around 350€. But a T245 handle and a C245 cartrisge cost only around 100€. So I figured, that if I can build a controller for under another 100€, it will make sense.I have analyzed all the info that I could find (teardown video, some closeup photos, a cartridge crosssection done by some chinese guy and this thread:http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=5264over at dengerousprototypes forums. I came up with block schematic like this:This is where I am right now:This is a very solid piece of ziptie engineering, but it's just temporary.Power supply:I's based on a huge 300W 12V halogene transformer, which I've bought for a few euros a few years ago. It will power the heater. This one is just temporary, as the original JBC uses a 150VA one with 23.5V secondary. 12V is being used instead of 24V, because I already had the transformer and because I could find parts that would work at 24V in my stash. Logic part is powered from a separate small 12V transformer (no idea where it came from). In final design I'll use either custom wound one, add my own low power winding by hand to an off-the-shelf transformer or use 2 separate ones.AC switch (bottom of the stack):It uses 2 back to back connected N-MOSFETs same as the original JBC. I didn't have enough info (photos etc) to clone the drive circuit, so I came up with my own. It uses a charge pump and two optocouplers - one for turning the FETs on and the other for turning them off. I'm pretty confident, that original station uses something along those lines too (2 optocouplers can be seem on the teardown video). Entire prototype is made out of junk: mosfets came from some PC motherboards, optocouplers from some blown SMPS. The rest is chickenfood. I have tested it with some power resistors, and it generally works as intended.Logic power and zero crossing detector (2nd from the bottom):Pretty simple 30V linear preregulator (zener + power transistor) to protect the circuit from surges and higher transformer output voltage when lightly loaded (an idea borrowed from user sparkybg over at DP forums), followed by an MC34063 (from junk pile) which is calculated for 6V@400mA output.This board also contains a zero crossing detector which uses a full bridge and an optocoupler to generate positive spikes at zero crossing. I may change this to omit the optocoupler and sense the zero crossing from the transformer that powers the control logic.Thermocouple amplifier and voltage reference (top board):This one is not finished yet, as I don't have the opamp (MCP6V02) and cold junction sensor (MCP9701A). It has it's own 3.3V supply and a reference voltage source (TL431 - from junk). I expect to finish that until the end of this week.CPU:CPU is gonna be a Cortex-M0 (STM32F030). This board contains an STM32F051, but it's not a problem, since F03x and F05x are pin to pin compatible.Interface:Right now I'm working on the interface, which will comprise of 3 7-segment displays for temperature readout, and a rotary encoder for temperature setting.The only relatively non-jellybean components are the MCU and the thermocouple opamp.I'll post some updates as I go.

author: bdivi
author_rank: Regular Contributor
timestamp: May 28, 2014, 03:37:55 pm
content: Why not just replicate the project from Dangerous Prototypes ?I have one working and the parts cost is around EUR20. Hardware and software are open so you can play with as much as you want.

author: SeanB
author_rank: Super Contributor
timestamp: May 28, 2014, 03:46:15 pm
content: If you look at that secondary you will find it is made from 2 parallel wires, so you can rewire it to give you a 24VAC power rail and have a centre tap as well to power the logic with a simple half wave rectifier.

author: Dago
author_rank: Frequent Contributor
timestamp: May 28, 2014, 07:12:39 pm
content: Quote from: bdivi on May 28, 2014, 03:37:55 pmIt is not for a JBC handle. They have an integrated thermocouple where you need to stop heating every once in a while (usually on mains zero crossings) to read the temperature. This enables the thermocouple to sit very close to the tip.That is the reason why JBC is so good

author: amyk
author_rank: Super Contributor
timestamp: May 28, 2014, 08:18:38 pm
content: Looks similar to the Hakko T19 scheme, same thermocouple+heater style. Maybe this controller would work too:https://www.eevblog.com/forum/reviews/interesting-936-to-t12-(fx951-integrated-tip)-conversion/

author: poorchava
author_rank: Super Contributor
timestamp: May 28, 2014, 08:19:03 pm
content: sparkybg from DP forums is working on what he calls "UniSolder" which is capable of using Hakko T17/T19, JBC C245 and even JBC tweezers. I like his ideas and I have borrowed a few of those (like the thermocouple amplifier selection for example) but it's too complicated. It also feeds the heater with rectified but not filtered voltage, which means large drop on the diode bridge - I believe my design is much more efficient. I also aimed at using as generic parts as I could - MC34063 for the switcher, TL431 for reference voltage, LM1117 as LDO and so on.@amyk:yeah, it's similar, but the internal connections of the tip are different and thermocouple too. I don't remember specifics, but I believe the difference was, that the heater was actually grounded (i.e. connected to outer sleeve of the tip) and so was the thermocouple, which makes things easier. You can see on the picture in first powt, that JBC kind of turned that around. If the inner sleeve was on the outside (and hence - system ground), this would have been the same as Hakko.As for the winding - it's not bifiliar, but rather trifiliar (3 wires in parallel), but they are wound as single output. If the insulating enamel on the magnet wire is not damaged, it may work. The I'll check that tomorrow.

author: SeanB
author_rank: Super Contributor
timestamp: May 29, 2014, 07:11:34 am
content: Thought as much, it is hard to wind a toroid with thick wire, so they often have a few in parallell. You likely can then use one as the logic supply and the other 2 in series for the heater supply. You will easily have enamelled wire insulation that will withstand 50V between the windings.

author: poorchava
author_rank: Super Contributor
timestamp: May 29, 2014, 12:31:58 pm
content: I generally had in mind, that this transformer has seen A LOT of abuse over past few years, including some dead shorted loads, overheatings etc, so the insulation may have been damaged.

author: SeanB
author_rank: Super Contributor
timestamp: May 29, 2014, 01:22:05 pm
content: Any insulation degradation would be a lot more likely to result in a shorted turn. Very noticeable as a burnt out transformer.

author: Rufus
author_rank: Super Contributor
timestamp: May 29, 2014, 01:56:13 pm
content: The most difficult part of a driver for JBC cartridges is the thermocouple amp.In the configuration you have the amp has around +/- 1.5v on its input while you are driving the heater. If you don't turn off the MOSFET switch exactly at zero current you get an inductive spike from the leakage inductance of the transformer some of which the amp will get to see. The amp needs to recover from these overloads before you can measure temperature and you have to hope the gross overloads don't upset the internal auto-zeroing.For the best temperature control you need to measure on every mains zero crossing and quickly decide if the heater should be driven for the next half cycle or not.The cold junction for the thermocouple is at the hand piece cartridge contacts. The hand piece warms significantly. A guess at hand piece temperature from a thermal model in software would do more than cold junction compensation on the control PCB. Taking a general ambient temperature into account in the model would help a bit.

author: poorchava
author_rank: Super Contributor
timestamp: May 29, 2014, 06:12:57 pm
content: Quote from: Rufus on May 29, 2014, 01:56:13 pmThere is a clamping circuit on the input consisting of series resistor and schottky diodes to ground to shunt anything >0.3V or <-0.3. At those consitions the output will obviously saturate, but I think that the opamp will manage that. We'll see when I get the parts.Quote from: Rufus on May 29, 2014, 01:56:13 pmI plan on synchronizing entire logic to mains crossings. uC will run from internal oscillator, but measurement and everything else will be done on mains crossings.Quote from: Rufus on May 29, 2014, 01:56:13 pmThe sensor on the board is indeed more for ambient temperature than anything else. I think it's possible to estimate temperature of the handpiece junction based on ambient temperature, time since the tool was picked up from the stand and tip temperature.It think it may also be the case, that the contacts inside the handpiece are the same metals as used in the cartridge, in which case there would not be any cold junction inside the handpiece, and the real cold junction would be at the connector.

author: poorchava
author_rank: Super Contributor
timestamp: May 30, 2014, 07:30:40 am
content: Interface board is ready.Display is a common anode type. Drive circuit is a standard one: BSS84's for switching anodes, 74HC595 for driving segments. Current limiting resistors are 160R (entire thing runs at 3.3V). There is also a rotary quadrature encoder with a pushbutton and 5 LEDs for debugging. Now I will start wiring up the uC board. Despite STM32F0 being able to progrtam it's own flash I plan to have an external eeprom for calibration data and storing temperature.

author: amyk
author_rank: Super Contributor
timestamp: May 30, 2014, 12:03:22 pm
content: QuoteLooking at the diagram again, it seems you have heater, thermocouple, and common connections to the tip, which means the controller design won't be much different from the 936 clones that use a thermocouple too. At first I thought it was more like Hakko's integrated tip which has only 2 terminals and the thermocouple and heater are wired in series.I think a triac would be better for control than a MOSFET, since they turn off automatically at the zero crossing.

author: poorchava
author_rank: Super Contributor
timestamp: May 30, 2014, 01:17:59 pm
content: Another update: the amplifier arrived and I have put it all together. The circuit generally works, but my choice of BAT54 as input clamping diode seems to be poor. The one which is connected with anote to siangl line and cathode to ground is leaking quite a lot and it loads the thermocouple. I will have to find another diode or use much larger series resistor. Other than that the amplifier works so far. I will post pictures later.Btw, I've made an error on the diagram in first post, inner sleeve and central rod ('core') are the other way around, so the thermocouple voltage must be measured between outer sleeve and the central rod.Choice of mosfets instead of triac mau have been for two reasons: One - triacs have higher voltage drop than 2 mosfets in series do. Second - you cannot control triac turnoff time. You'd have to turn on somewhere in the middle of the cycle, and then triac would conduct until voltage falls below threshold. With mosfets you have complete control over turn-on and turn-off events.

author: C
author_rank: Super Contributor
timestamp: June 01, 2014, 03:45:14 pm
content: Just some IdeasWhat if you added a balanced RFI/EMI filter. The ac switch and transformer winding on one side. The amp and the leads to the tip on the other side.Should remove some of the ringing and transient noise from the amp.Next I see an AC signal that is offset from ground by a DC signal. The average of an AC signal is 0 so by averaging samples you would get the DC signal.If you added some Active cancellation to the amp you could keep the signal in the input range of the amp.How much does the heater resistance change with temp? If you had some feedback the heater temp could help make fast temp changes better.C

author: poorchava
author_rank: Super Contributor
timestamp: June 01, 2014, 06:30:46 pm
content: I think that for maximum rms currents over 6A the filter would be seriously large, but I'll look into that.AC signal is offset from system ground only by the thermocouple voltage. The voltage drop across wires is around 25mV or so at 2A through the heater. As for the heater resistance temperature coefficient, I'll check and see.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: June 02, 2014, 06:08:18 pm
content: Probably not what you want to hear, but but just for info: you can get a new JBC station with T245 handpiece plus two cartridges for less than 250€...Ok, it's analog but still tempting.eBay (including VAT and shipping in Germany)http://www.ebay.de/itm/JBC-Lotstation-BT-2BWA-analog-mit-Lotkolben-T245-A-und-Zubehor-/231246976280Webshop (including VAT, excluding shipping)http://www.chiemtronic.de/produkte/jbc-loetstationen-loettechnik/analoge-jbc-loetstation-bt-2bwa/

author: poorchava
author_rank: Super Contributor
timestamp: June 08, 2014, 11:20:23 pm
content: A small development:The ac switch and zero crossing detection is fully working. I also wrote software to control the display and the encoder (which turned out to be really crappy and required additional filtering and an external schmitt trigger). I still have some glitches at minimal and maximal duty cycles, but those are only software quirks.Now I have the analog part left.

author: poorchava
author_rank: Super Contributor
timestamp: June 13, 2014, 06:09:46 am
content: Yesterday I found some time to work on the project. Right now the setup looks like this:I have put entire circuit together more or less. Some conclusions:-zero crossing should be sensed from the same winding which powers the tip. Sensing from another transformer (the small one that powers logic) introduced phase shift between the zero signal and the actual zero.-the opamp behaves well when driven into saturation and desaturates reasonably quickly. I may add some load th the opamp output to speed up coming out of positive saturation-replacing BAT54 with 1N4148 as opamp input clamping diodes helped.-I must have miscalculated necessary gain, because the opamp hits the rail at about 300 degrees-powered from 12V transformer, this is already powerful as hell and heats up fast-analog part is quite stable even without software avaraging , i'm getting about +/- digit readout fluctuationInteresting part:JBC tip CAN be used as a weak substitute for a light bulb. By some software bug I have managed to get the tip glowing hot. And it still works wihtout proble and is still getting wetted by solder perfectly. This stuff is really impressive... I added a block of power resistors in series though, to limit the power.

author: poorchava
author_rank: Super Contributor
timestamp: June 15, 2014, 04:38:20 pm
content: It works! Right now only with very crude proportional regulator, but it keeps the temperature within 2 degrees from setpoint.I will now look for an enclosure and design the board for ordering :-)Would anyone be interested in buying a pcb, a kit or a fully built station? I won't be asking alot, just to return the material and shipping costs.

author: bitshape
author_rank: Contributor
timestamp: June 15, 2014, 05:38:54 pm
content: Quote from: poorchava on June 15, 2014, 04:38:20 pmIf you keep it very low, there could be someone here (not from Europe) who wants to buy a kit.Because in Europe you can get the analog JBC BT-2BWA with Handle & 2 chisel Cartridges for 249,- Euro's. Without the Handle and the 2 Cartridges you pay plus/minus 150 Euro's. The station is new and fully factory warranted.I'm personally more interested in a analog BT-2BWA or digital CD station hacked to use with the 2 JBC TweezerTools.Quote from: 0xdeadbeef on June 02, 2014, 06:08:18 pmAlso available here:http://weidinger.eu/shop/loettechnik/jbc/jbc_loet-_und_entloetgeraete/jbc_loetstationen/wl26830

author: dannyf
author_rank: Super Contributor
timestamp: June 15, 2014, 05:51:08 pm
content: It seems very complicated. I have done solder stations with A1321 handles (4 wire, with thermcouple as a temperature sensor). Power comes from a laptop power supply (20v), and NE5532 as the thermocouple amplifier (with some avrs having 20x / 40x adc, you don't need that amplifier at all). No display however, other than an RGB led to indicate status.Temperature kept within a 1c or so.I may build one with 4-digit led display just for fun - the firmware is already written.

author: poorchava
author_rank: Super Contributor
timestamp: June 15, 2014, 06:00:56 pm
content: It is not complicated. It's only a prototype, so it looks the way it looks. Esentially it's 2 MOSFETs, 3 optocouplers, an opamp a microcontroller, some shift registers, basic power supply and a handful of passives.

author: poorchava
author_rank: Super Contributor
timestamp: June 15, 2014, 06:51:10 pm
content: Quote from: bitshape on June 15, 2014, 05:38:54 pmDunno if you're joking or not, but hot tweezers are from hardware standpoint two separate tips

author: bitshape
author_rank: Contributor
timestamp: June 15, 2014, 07:03:05 pm
content: Quote from: poorchava on June 15, 2014, 06:51:10 pmNo, not joking.Read more carefully what i said.And maybe you can make your controller compatible with the JBC Tweezer-tools, or must i buy and use 2 separate controllers from you for one tweezer-tool (with 2 tips)?

author: poorchava
author_rank: Super Contributor
timestamp: June 15, 2014, 08:32:08 pm
content: I will look into that. In principle this should not pose much problem. It will require additional set of MOSFETs and optocouplers. Opamp that I chose is already a dual channel one, so no problem there.I think my project is quite economical:T245 handpiece - 63€ (TME)some tip, eg C245939 - 35€ (TME)24V, 150VA toroidal transformer - 19€ (toroidy.pl - local Polish manufacturer), almost any other transformer can be used (i use 12V/300VA in the prototype and it works just fine)STM32F051K6 - 2.5€ (Farnell)RPC1-6RB-12P connector - 2.8€ (Farnell)PCB - ~2€/piece from Elecrow if it fits on 10x10cm formatMCP6V02 opamp - 2.2€Enclosure -http://www.kradex.com.pl/shop?product=287Local Polish manufacturer, they have english version of the website but i dunno if they ship abroad. If anything, I can buy and distribute that to people. Anyway - appropriate enclosure is under 2€.Other bits and pieces like displays, encoder, optocouplers, trimpots and the like can be had from anywhere or from junk, so I won;t bother listing them, as anybody probably has them in their junkpile. So the control units sums up to 30€ for major components. Even assuming that the rest will cost another 30€, this is still cheap

author: tautech
author_rank: Super Contributor
timestamp: June 15, 2014, 08:57:39 pm
content: I love a good rats nest.Keen to see your finished PCB.

author: dannyf
author_rank: Super Contributor
timestamp: June 15, 2014, 09:04:48 pm
content: QuoteI think I can get mine under $10:mcu: <$2.led display: <$1.mosfet: <$1.encoder: $1.misc. parts: $1.laptop power supply: free.

author: poorchava
author_rank: Super Contributor
timestamp: June 15, 2014, 10:02:03 pm
content: I don't doubt that, but JBC T245-A handpiece and C245 cartridges are superior to hakko, especially when it comes to power and ability to handle large thermal masses which is important to me as I do quite a lot of power electronics.

author: poorchava
author_rank: Super Contributor
timestamp: July 20, 2014, 12:36:09 pm
content: Some update.I have selected an enclosure and made a PCB for it.I'm hoping to order the PCB some time soon.

author: bdivi
author_rank: Regular Contributor
timestamp: February 03, 2015, 11:00:22 pm
content: Long time no newsany update with this project ?

author: poorchava
author_rank: Super Contributor
timestamp: February 04, 2015, 12:30:05 pm
content: It's on hold right now.I've assembled most of the circuit (excluding the thermocouple interface section) and the project has been put on hold due to shitload of commercial work. What's done so far:-power supply is working as it should-uC works and communicates with debugger-led display works and displays garbage as expected (segment connections have been changed since the prototype but code was not updated)-AC switch works after some modification that involved getting rid of PNP transistors that were driving mosfets. Right now mosfets are driven by optocouplers directly. The optocouplers I chose have proven to have too high dark current and small signal PNPs with high hfe would turn on spontaneously-zero detection works after a little 'woops' which involved a double diode in a diode bridge being put onto schematic in reverse direction, and this resulted in sudden disappearance of the diode together with a few milimeters of pcb track. Anyway - it works now.I'm gonna work on it further, but right now I'm sleeping 2-3 hours a day and have no time to work on private projects.

author: dom0
author_rank: Super Contributor
timestamp: March 03, 2015, 07:43:31 pm
content: Do you know what kind of connector they use and if it's available commercially?Could you confirm if the cold junction is indeed in the hand piece (or in the connector)?I'm currently thinking about something similar, since I have most of (the cheap) parts for something similar at hand (power supply, some chopper op amps, and the usual other stuff). But I'd use one of the laptop supplies from my stock (have plenty of 60 and 90 W bricks) for the power part. Heating with DC shouldn't be an issue and saves one switching element plus the opto-couplers and zero-crossing detection stuff.

author: ajb
author_rank: Super Contributor
timestamp: March 03, 2015, 08:24:12 pm
content: The connectors are Hirose RPC1. They're available for a few bucks in single quantities from Mouser.I've had a T245 handle and panel mount connector sitting around for several months for a similar project, just haven't gotten around to doing much of anything with it.Regarding using a DC supply, I've read in other discussions some warnings that using DC can shorten the life of the heater due to electromigration, but I haven't really seen any specifics as to how substantial the loss of lifespan is, or if electromigration is even a concern with the types of heating elements JBC uses. The JBC cartridges are expensive enough that saving two or three cartridge replacements over the lifetime of the base station probably justifies the extra cost of using an AC supply. On the other hand, the cartridge replacements would be a deferred expense...

author: poorchava
author_rank: Super Contributor
timestamp: March 03, 2015, 08:51:20 pm
content: Yep the connectors are available.As for the cold junction compensation, I'm almost sure that there is none in the handpiece, unless they somehow use the handpiece-cartridge connection as a thermocouple (I don't know how feasible is that and what is the contact material). Since they sense the handpiece being put in the stand, they might be compensating somehow based on how long the handpiece has been held in hand, but this would only be a very minor adjustment.DC heater drive would be fine if synchronous rectification was used, such as the Linear replace-diode-bridge-with-mosfets chip. Otherwise rectifiers would dissipate a good few watts of power. Schottky rectifiers are no good, as they usually have relatively high reverse leakage current, which would distort thermocouple readings. The heater switch needs to be really high impedance in the off-stage. The AC switch which I have developed is cheap, simple and the power dissipation is negligible. The only important point is that the optocoupler collector-emitter voltage has to be higher that peak AC voltage.I really regret not being able to work on this project right now, as I could REALLY use a new iron.

author: dom0
author_rank: Super Contributor
timestamp: March 03, 2015, 09:27:11 pm
content: With a floating heater supply a standard N-Ch MOSFET should do the trick, given that the heater supply (and thus Vgs) is only floated by thermovoltage

author: poorchava
author_rank: Super Contributor
timestamp: March 03, 2015, 09:39:32 pm
content: The switching element has to have a high off-state impedance, because the switched end of the heater is the thermocouple connection at the same time, so a slightest current flow will throw off the measurement, as the thermocouple is not particularily sensitive (like 2.8-3mV @ dT=300 deg.C) the amplifier has really high gain (in the order of several hundred). The floating gate drive storage capacitor is fed through the parasitic body diodes of the mosfets, so the temperature measurement must occur near zero-crossing, because at that moment the charge pump does not draw current through body diodes, and also interferences are at their lowest.

author: fredboivin
author_rank: Regular Contributor
timestamp: June 04, 2015, 07:41:03 pm
content: Hi, very interesting project!Do you know how JBC does its sleep and tip changing poweroff? In the UniSolder, Sparkybg does it with an IR sensor, but I'd like to know how has JBC implemented it.Thanks!

author: savril
author_rank: Regular Contributor
timestamp: June 05, 2015, 12:52:45 am
content: Quote from: fredboivin on June 04, 2015, 07:41:03 pmWatch Dave tear-down video on the JBC. The iron holder has a wire that get it linked with the base station. When the iron is in the holder, the iron touch a metallic surface. So it is as simple as detecting that the metal in the holder is connected to ground. When you see that other shops are using accelerometers for that.For the tip, it detect that there is no resistance (by current measurement ?). In Sparkybg design, he use the resistance to differentiate the different irons and it also detect the tip changing (but for JBC it's not named tip but cartridge because it contain the heating element).

author: fredboivin
author_rank: Regular Contributor
timestamp: June 05, 2015, 02:01:49 am
content: Ahhhh, I must have missed it! I should have known a reputable company like JBC would keep it stupid simple.But, isn't the cartridge at 180degC? How do they keep that wire from heating up?Thank you very much!

author: poorchava
author_rank: Super Contributor
timestamp: June 06, 2015, 12:47:36 pm
content: I have no idea to be honest. My best guess is that connections between the cartridge and the handpiece have low ohmic resistance, but rather small cross section and therefore thermal coupling is not very good.On the other hand JBC really knows metallurgy. On one occasion by a mistake in the software I got the tip to white-hot-and-glowing state, and after it has cooled down it still worked ok...Wys?ane z mojego GT-I9100 przy u?yciu Tapatalka

author: fredboivin
author_rank: Regular Contributor
timestamp: June 06, 2015, 01:42:12 pm
content: I looked a little more at the handpiece anatomy and noticed that it's the metal ring at the end of the piece (which is not supposed to get hot) that acts as a contact for the sleep mode. The cartridge changing tool is wired to another pin, but doesn't get hot because the tip isn't heated anymore.

author: Didgitalpunk
author_rank: Contributor
timestamp: July 26, 2015, 04:53:28 pm
content: Very cool project! can't wait to see it finished.Btw, when you have time, would you mind sharing thePCB layout files and parts list?schematics? I'm quite interested to do one myself and I think quite a couple folks here are as well

author: timofonic
author_rank: Frequent Contributor
timestamp: August 20, 2015, 02:21:51 am
content: Any news about it? JBC are nice, buy their stations are very expensive.They are from my country, Spain. I'm happy there's something good here...

author: poorchava
author_rank: Super Contributor
timestamp: September 25, 2015, 08:25:59 am
content: Heh, still no time to finish the project. I'm working on it hour or two a week, but unfortunately I can't devote more time to it.But no fear, the project is definitely not dead.Sent from my HTC One M8s using Tapatalk

author: cam
author_rank: Newbie
timestamp: November 25, 2015, 07:12:11 pm
content: Hi,I actually own a JBC BT-2BWA which is the analog version of the CD-B. I am more into the analog one because I believe it is easier to set the temperature with it but unfortunately it doesn't has the temperature reading.I googled around for infos about where to read this temperature so I could build a display (most likely with 7 digits displays) and guess what... I found your topic which looks the most detailed about the T245 pencil. First I'd like to thank you for sharing what you're building, it is well regarded as JBCs costs a lot but are THE soldering stations!Now, I was wondering how you read the temperature from the connector? I didn't get much time to go through the design of a soldering station since I own a good oneYour input would be much appreciatedThanks!

author: poorchava
author_rank: Super Contributor
timestamp: November 25, 2015, 07:48:29 pm
content: There is an mcp9700 temperature sensor on the PCB near the openocd for the connector. The sensor is THT so it may be mounted on the connector itself if need be (not sure what would the fastening metod be though).Sent from my HTC One M8s using Tapatalk.

author: cam
author_rank: Newbie
timestamp: November 25, 2015, 08:02:27 pm
content: Thanks for the fast answer.I'm not sure how it is supposed to work, MCP9700 seems to work from -40C to +150C.How is it suppose to measure up to the 450°C the soldering station can do?

author: poorchava
author_rank: Super Contributor
timestamp: November 25, 2015, 08:33:21 pm
content: Umm, the MCP9700 is for cold junction compensation. The connector which is in the handpiece is not accounted for. I think that if we assume that all the contacts are at the same temperature and the emf generated across them is similar, then they will compensate one another. Also, the thermal isolation between heater and the contacts is excellent. I could have the tip at 350 deg.C and I could hold the other end of the cartridge with my bare hand it was only a bit warm.Also, I don't think It very important for a soldering iron to be accurate to half a degree or something. I assumed that +/-5 degrees is perfectly fine.Sent from my HTC One M8s using Tapatalk.

author: cam
author_rank: Newbie
timestamp: November 26, 2015, 06:18:42 am
content: Thanks again for the fast answerSorry I don't know much about this component I did not know about which made ask stupid question.I looked at the datasheet and basically I just need to find a suitable uC with a ADC input to feed the 7 segments. it's just a matter of converting the Vout pin of the MCP9700 to binary. There is no compensation to take care of if I use the Vout pin of the MCP9700 because it is what is used for the regulation in JBC electronic card. Did I get it right?Thanks again, your topic convinced me I can, without too much trouble, add a digital display on my station.I'll post update later when I have time to work on it.

author: poorchava
author_rank: Super Contributor
timestamp: November 26, 2015, 08:40:44 am
content: Yes and no.The tip contains a thermocouple between the heater element and the shield.Thermocouple as such allows to measure only difference of temperature between two ends, not the absolute temperature. You need to know the temperature of one end (cold junction), to calculate the temperature of the other end (hot junction). This is what MCP9700 is for.And yeah, I'm reading the temperature by uC and then displaying it, but it's not enough to just turn on/off the heater. First of all you need to switch on slightly after mains zero and switch off slightly before it in order to measure the thermocouple voltage exactly in the zero. Also, the duty cycle once heated up is pretty low, as the JBC cartridges) are rated at 130W peak power (IIRC) and the transformer such as that used in original station would in this situation deliver over 300W if turned on permanently.The switching circuit is a bit convoluted, because it uses MOSFETs to switch AC in order to reduce losses (as compared to switching rectified DC). Triacs/thyristors are not an option, because they cannot be turned off before zero in a controlled manner.

author: cam
author_rank: Newbie
timestamp: November 26, 2015, 05:36:24 pm
content: I'm a bit confused.All I would like to do is to read the temperature from its most suitable pin wherever it is on the JBC PCB and then convert it to binary in order to display it on three 7 segments digits. Even if this means doing math in the uC with this value then convert to binary.I thought I would need one input for the analogue value (temperature of the pencil) and 21 digital outputs for the 7 segments displays and their shared ground. Isn't this correct?

author: poorchava
author_rank: Super Contributor
timestamp: November 26, 2015, 05:43:32 pm
content: No that easy. Since temperature is measured by a thermocouple which has very low signal level, no current may be flowing through the same wire during measurement. Since the cartridge has only 3 contacts, then at least one of them is shared between the heater and the sensor. This means that you have to synchronize your heater drive with temperature measurements. Also, since the heater is powered from unrectified AC, best moment to switch stuff and make sensitive measurements is near zero crossing.Cold junction compensation is mandatory. That's just how thermocouples work.BTW, 3 digital of 7seg display only need 10 digital pins if not using digital point. Multiplexing is the way to go. This can be bought down to 3 pins if need be (Multiplexing + shift registers).Sent from my HTC One M8s using Tapatalk.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 26, 2015, 05:50:27 pm
content: Quote from: poorchava on November 26, 2015, 08:40:44 amQuoteor you could skip an entire mains half-cycle to do the measurementQuoteThough for the accuracy needed in a soldering iron application, just assuming the CJ is always at about 20 deg.C, or using a very simple/cheap ambient temp sensor isn't going to affect things enough to be a problem in practice.

author: cam
author_rank: Newbie
timestamp: November 26, 2015, 06:03:32 pm
content: Quote from: poorchava on November 26, 2015, 05:43:32 pmAs I understand, I need to know the heating signal and Vout of the MCP9700 as inputs. Would have been too easy if it was only a matter of convertionQuoteI didn't got much into it and I assumed there is one input pin for each LED (I do not count Vcc and GND because they don't use uC outputs) but it may be different in practice. I'll check the datasheet later when the rest is clearer in my mind.

author: poorchava
author_rank: Super Contributor
timestamp: November 26, 2015, 06:04:00 pm
content: Agreed, MCP9700 is just that, cheap and simple (and I already had it in my drawer). Any other popular temperature sensor could be used: LM35, DS18B20, thermistors, diode forward voltage etc...Assuming that CJ is always at some fixed temperature might introduce big errors. For example in my workshop the soldering station base unit is stadning in a shelf of sorts with lots of other gear, so the temperature there is most definitely not the same as room temperature.@cam:You need to know when the mains zero crossings are, make sure that the heater drive is off, measure the thermocouple voltage and then drive the heater. Cold junction temperature can be sampled at any moment convenient.Sent from my HTC One M8s using Tapatalk.

author: timofonic
author_rank: Frequent Contributor
timestamp: January 04, 2016, 09:53:38 pm
content: Any progress on this?

author: x_dadu
author_rank: Newbie
timestamp: September 24, 2016, 04:16:24 pm
content: What type of termocuple this JBC C245 has ?

author: tcurdt
author_rank: Contributor
timestamp: April 06, 2017, 04:08:02 pm
content: Are the schematics online somewhere?I am wondering about the AC vs DC choice.Are the losses really that big at e.g. 120VA?

author: Icchan
author_rank: Regular Contributor
timestamp: January 21, 2020, 09:22:16 pm
content: Could you please move your images to imgur instead of photobucket? They're blurred out and one can't even visit the photobucket site with adblocker on :/Best case would be you to upload them to the forum directly... but hmmh...