Sewing Machine Simulator

First of all a word of warning! Remember that it is absolutely mandatory that you know what you do when repairing on or tinkering with devices operating on mains voltage, no matter whether you do that in a 230 V or in a 115 V country. Mains voltage can cause an electrical shock that is extremely unpleasant at best, but can kill you at worst. ALWAYS disconnect the unit from the mains before touching anything inside it.

Learning by doing might be too slow!

I volunteer in the non-profit repair shop of a community centre, and from time to time a sewing machine is brought in. In some cases the owner has troubles operating the machine because she/he didn’t bother following the !#@&ing manual, and sometimes the machine just wasn’t sufficiently cared for – because older sewing machines, in particular, are marvels of precision mechanics, and as such they need some TLC. The right amount of the right oil, in the right moment and in the right places (yes, there usually are lots of different lubrication spots hidden under the covers) is mandatory and can perform wonders – a procedure that is, of course, covered in the respective operating manual.

But if there is a problem with either the cable or the ‘gas pedal’ rather than with the machine itself, lugging the heavy machine to our shop for a repair or check-up isn’t really necessary.

A sewing machine foot pedal is in fact nothing but a kind of (mechanical or electronical) light dimmer. There are a few little differences, because driving an AC motor is a bit more demanding than dimming an incandescent lightbulb. Such a dimmer pedal can, as every other electrical/electronical component, fail after years of use. Connecting cables, too, can be ailing after year- or even decade-long (ab-)use. With the right adapter, it is possible to troubleshoot a suspect cable/pedal assembly in (y)our workshop without having to lug around a heavy sewing machine, therefor I call this the ‘sewing machine simulator’.

Early sewing machines from the 1960s (such as the beauty that I inherited from my mom, see above) are equipped with the stone-age, mechanical rheostat that is enclosed in a ceramic case. It contains one or two columns of many, thin (about 0.5 mm) graphite pills that have a high electrical resistance when in their relaxed rest position. The more pressure is exerted on them, the smaller the resistance becomes, and so more current can flow from the mains outlet, through the pedal, to the machine’s motor. The concept can work reliably for decades, but generates heat in operation and hence is not too energy-efficient. This kind of pedal is still available today as a quite inexpensive, but perhaps not too reliable replacement – as long as you know how to connect it to the machine.

Later machines came with more or less sophisticated, electronical pedals, some of them needing an additional live wire for supplying the electronics (identifiable by a three-wire cable or a three-pin connector), some of them doing without it (two-wire cable or two-pin connector). This kind of pedal as well is available as a quite inexpensive replacement – again, as long as you know how to connect it to the machine.

Unfortunately, most sewing machine manufacturers chose to design their own, specific connectors, not least for safety reasons. Therefor, replacing a cable or a pedal is usually becoming more difficult the older the machine is, because these connectors are hardly available as spare parts, if at all, and often only complete with cable(s) and usually the pedal. Of course, the manufacturer prefers selling a new machine to supplying a replacement pedal or even a replacement cable and/or connector. Even if a matching pedal and/or cable is available (or if you manage finding a second-hand replacement on an auction platform), this may become quite expensive. As already mentioned above, there are cheaper solutions available. I will mention some of these, and perhaps my own DIY pedal, towards the end of this Instructable.

Please note: Most modern machines, identifiable by a low-voltage pedal equipped with a plug similar to the one you know from your headphones, are NOT covered by this Instructable, because these machines have all the control electronics integrated inside their enclosure, if I understand correctly. Their pedals, as far as I know, only contain a low-voltage potentiometer. Once I should stumble upon such a machine, I might extend this Instructable accordingly.

In the following steps, I will show you how to identify and troubleshoot different cables/pedals of some of the popular (at least in my European region), earlier sewing machines, and how to cobble together makeshift adapters that allow you simulating these machines, mostly with materials from your junk box, for next to nothing.

Real-world cable and connector repairs are not the main focus of this Instructable, but I will mention one or two examples towards the end, just for your information, in case you should become curious.

Materials

1. Brass or even steel screws, e.g. M2 or M2.5, length about 20 mm – depends on the actual pedal/machine/cable combination
2. Pins harvested from an old IEC-320 appliance inlet – depends on the actual pedal/machine/cable combination
3. Perhaps two springy 4 mm ‘banana’ plugs from your junk box – depends on the actual pedal/machine/cable combination
4. An old (but working) 60 to 75 W incandescent lightbulb – yes, it has to be an incandescent bulb! You might, use an 80 W, linear, halogen bulb instead, since they are still available nowadays (but I don’t know for how long)
5. A socket for the lightbulb or an appropriate socket for the linear halogen bulb. In case of the linear halogen bulb, you must provide a contraption protecting the user (that is, you) from touching the halogen bulb, because in operation, they become VERY hot VERY quickly, and you never! must touch them with your bare hands, even while being cold
6. A piece of two-pole stranded wire
7. Wire-end sleeves
8. Some PS (polystyrene) sheet about 1 mm thick – perhaps pilfered from some packing material
9. Masking tape
10. Large heat-shrink tube (may be substituted by electrician’s tape)
11. Chopsticks
12. Polystyrene cement (as used for assembling model kits)
13. Hot glue sticks

Tools

1. Ohmmeter (or a multi-meter with Ohms range)
2. Continuity tester
3. Small screwdriver
4. Scissors
5. Wire cutter
6. Wire stripper
7. Crimping tool for wire-end sleeves (optional)
8. Hot glue gun
9. Hot-air gun

Soldering iron and solder

The wiring of household sewing machines usually follows three different, basic configurations, of which I show you example diagrams here. They are not too complicated and show not only the connection of pedal and motor, but also the sewing light that can be switched on or off, independent of the motor control.

1. Bernina machines from around 1960 (e.g. the 530 Record pictured in the introduction, and the early 730 Record versions) have two separate, dual-wire cables. One of them connects the machine to the mains outlet. The connector in the machine is similar to today’s IEC-320 male appliance inlet but has two pins only. The second cable is fixed to the pedal, it connects to the machine with a proprietary, two-pin, male plug, see diagram ‘Version 1’. Since the two cables are separate, no more has to be said about them here.
2. Later Bernina 730 Record models from the late 1960s have a single cable that is kind of a daisy chain; two dual-wire cables are joined at the proprietary female connector that is plugged into the machine. One of these cables goes to the mains plug, the other one is fixed to the pedal. See diagram ‘Version 2’. For these machines, inexpensive aftermarket replacement pedals can be found that are even equipped with connectors matching the machine.
3. Bernina 830 Record versions (beginning of the 1970s) are similar, but the pedal cable has an additional, proprietary, female connector that plugs into the pedal. See diagram ‘Version 2’. For these machines, inexpensive aftermarket replacement pedals can be found that are even equipped with connectors matching the machine.
4. Then there were the Bernina 802-803 series machines that featured electronic pedals for the first time (afaik). These pedal cables had a third wire because the electronics within the pedal needs supply voltage. The cable itself is a daisy-chain configuration, too, with a proprietary female connector that looks like it had four contacts, but only three of them are used. Two cables start there: a dual-wire cable that goes to the mains plug, and a triple-wire cable that plugs to the pedal, again, with a proprietary female connector. See diagram ‘Version 3’. Spoiler alert: Substituting such an original pedal by a modern replacement pedal that only has a dual-wire cable is possible without problems – the only thing you need to know is how to connect it.
5. I have one more cable/connector/peal combination in my collection from a Singer 8280 sewing machine that is younger but still about 20years old that seems to be very similar, if not identical, to the one I found on a ‘Durabase’ supermarket-brand machine of about the same age, if I remember correctly. This is as well a daisy-chain configuration, but with a different, proprietary female machine connector that, of course, doesn’t match any Bernina machine that I know of. The diagram ‘Version 2’ is valid for this connector type, too.
6. I will get access to a vintage, Swiss-made Keller sewing machine soon. When I have collected the information for its cable/connector/pedal, I will update this Instructable accordingly.

When comparing the diagrams of the three different versions in step 1, you can see that they are not that different.

To avoid misunderstandings: Please note that detecting the pinout of the machine connector only requires the cables and the pedal, but not the sewing machine.

Version 1 is the easiest to understand – there are two cables, one for connecting the machine to the mains outlet, and another one for connecting the pedal to the machine. The common conductor of the two cables connects via the machine, and there are, of course, two connectors, both of them with two contacts. The appliance inlet at the machine is male, and the plug on the cable from the pedal is male, too – so it is impossible to get zapped (or worse). In this case, nothing has to be detected because the two cables are clearly separated. And since we deal with AC (alternating current) here, there is no polarity to be observed.

Version 2 is almost identical, but the two cables – mains to machine, and pedal to machine – are combined at the single machine connector that has, now, three contacts. The common conductor of the two cables is connected within the machine connector rather than within the machine. There are different cases.

Regardless whether the pedal is mechanical or electronical, if there is an additional connector between pedal and pedal cable, it’s easy. You can find the contacts common to mains plug, machine connector and pedal connector with an ohmmeter or a continuity checker; the common contact at the machine connector is usually the centre contact.

In case of a mechanical pedal, if the pedal cable is fixed at the pedal, finding the common contact is not that simple. First, establish (using paper, pencil and a sketch of the connector’s front view) which two contacts of the machine connector are connected to the mains plug. Let’s assume the contacts #1 and #2 of the machine connector are connected to the two pins of the mains plug. Select the 1 kΩ or the 10 kΩ range on your ohmmeter and connect it between contacts #1 and #3 of the machine connector. If the resistance reading is infinity regardless of whether the pedal is pressed or not, contact #3 is not the common contact, but contact #2 is. If the ohmmeter reads between infinity (pedal not pressed) and some 10 to 20 Ω (pedal fully pressed), then contact #3 is the common contact. Usually, the centre contact, that is, contact #2, is common. To be sure, you might open the pedal carefully and check with the continuity checker which contact of the machine connector goes to both the mains plug and to the pedal. This is the common contact.

Worst of all is an electronical pedal with a fixed cable – then you cannot use the ohmmeter but must try to open the pedal carefully, that is, non-destructively, and check with the continuity checker which contact of the machine connector goes to both the mains plug and to the pedal. This is the common contact.

Version 3 is almost identical with version 2, but the pedal cable has three conductors for supplying the pedal electronics. I never met a pedal requiring the additional supply with a fixed cable, but identifying the common and the supply contacts on the pedal connector isn’t easy nevertheless. For this purpose, you either have to guesstimate, use trial & error, and/or you need access to manufacturer’s specs (that I fortunately had during repair of the Bernina 286 pedal supplied with the Bernina 802 and 803 ‘electronic’ machines).

Provided that the manufacturer didn't change wire colours during production, the wires for connecting a dual-wire pedal are black and brown. The third, blue supply wire is no more used, and its end must be insulated.

To simulate the machine for checking pedal and cable(s), you need a connector (or connectors) similar to the one(s) installed in the machine. They must, of course, match the machine/pedal cable connector(s). Unfortunately, these connectors are not available off the shelf, so you have to cobble them together by yourself. To make things easier, the simulator only needs two contacts, even if the machine connector has three contacts – with the exception of version 1 that needs both a two-pin ‘machine’ plug and a two-pin ‘pedal’ socket.

The two first pictures above show the connectors on my Bernina 530 Record machine with their matching plugs, first the connector at the rear of the machine that connects to the mains, then the one at the machine's right-hand side where the pedal cable is plugged in.

I will give you step-by-step instructions how I made the connectors for version 1. Some words about connectors for the other versions will follow.

First, the two-pin, male machine plug:

1. You need the female machine connector (picture #3) and a strip of polystyrene about 2.5 cm wide, 1 mm thick and long enough to fit two times around the machine connector. Tightly wrap the polystyrene strip around the end of the machine connector and use polystyrene cement on a length of about 1 cm at the beginning of the strip. Clamp together until the cement has set. Then coat the rest of the strip with glue and wrap the whole strip tightly; fix with some masking tape and clamp until the cement has set (picture #4). You can then pull this coil away from the machine connector.
2. Cut up an old IEC-320 appliance inlet (picture #5) to remove its pins (picture #6).
3. Strip the ends of a piece of two-wire cable, then tin and solder them to the two shorter pins (picture #7).
4. Cover the ‘business end’ of the machine connector with masking tape and cut it to shape. Cut two slots into the tape where the pins will go in (picture #8). Thanks to the masking tape, the machine connector used as a template and the new plug will be easier to separate later.
5. Slide the polystyrene coil over the end of the machine connector so that about 10 to 15 mm of the coil project over the end of the connector. Firmly push the two pins with the connected cable into the two slots (picture #9).
6. Fill the hollow inside the polystyrene coil and around the ends of the pins with hot glue and let it cool down (picture #10). Only after it has cooled down completely you can separate your new connector from the machine connector – which might require some gentle violence.
7. You may want to slide some large heat-shrink tube over the polystyrene coil that extends towards the rear. Shrink it with your hot-air gun. Once it has cooled down, fill the gap between the cable and the end of the heat-shrink tube with some hot glue as a kind of makeshift strain relief (picture #11).

Then, the two-pin, female pedal socket:

1. The pedal plug has two pins with a diameter of 4 mm (picture #12). To contact these, I used two old, hollow ‘banana’ lab plugs by ‘Stäubli MultiContact’ that are springy enough to accommodate and reliably connect to the 4 mm pins of the pedal plug (picture #13).
2. Strip the ends of a piece of two-wire cable and solder them to the end of the two lab plugs (picture #14).
3. Cover the front of the pedal plug with masking tape (picture #15).
4. Plug the two lab plugs with the cable end onto the pedal plug (picture #14 again).
5. Put a piece of tube with sufficient diameter over the lab plugs and temporarily fix it to the pedal plug. This piece must be somewhat heat resistant because it will be filled with hot glue; I used the inner cylinder of a roll of adhesive tape and didn’t check for stability; after filling it with hot glue it immediately went soft and shrank faster than I could watch – not so good (picture #16).
6. Fill with hot glue and let cool down. My ‘socket’ was really ugly and smaller than planned (picture #17).
7. Slide some heat-shrink tube over the assembly and shrink it with your hot-air gun. Again fill the end of the heat-shrink tube with hot glue as a kind of makeshift strain relief (picture #18).

For producing (male) connectors matching different machine connectors, some imagination and improvisation is required. The principle is similar as given above – use the cable’s (female) machine connector as a template and find matching contacts (I used pins harvested from IEC-320 appliance inlets again, but also screws with matching diameters, M2 and M2.5 in two cases); the cable can be connected by soldering or by using solder lugs fixed to the screws with a nut and perhaps serrated washer.

All these connectors have special outlines and also recesses that protect them from being plugged the wrong way round, and these must be modelled as well. I again used polystyrene sheet for the outline, and the smaller ends of chopsticks to fill in the recesses. To mechanically fix and at the same time electrically insulate the pins and the chopstick ends, I recommend hot glue here as well. You will find pictures of some of these connectors from my collection later a little later.

The heavy lifting happened in the last step, now it gets easy. Let’s continue with the example from step 3 with two separate cables for the machine and the pedal connectors, see the ‘Version 1’ simulator diagram above.

1. You have two short pieces of cable with the new custom connectors on one end, the other ends still are free. Strip both ends, twist one wire of each cable (in my example, the blue wires) together, and solder (picture #2 above). The two other ends should be provided with wire-end sleeves – if you closely watch the picture, you can see that the brown wire ends are not soldered. There exist tools for crimping wire-end sleeves, but don’t worry if you don’t have one. You can also give them a few careful nicks with your wire cutter, because they just should be fixed a little on the wire until they are clamped in the simulator.
2. Bend the two connected wires backwards and insulate the soldered end with a bit of heat-shrink tube (pictures #3 and #4).
3. Connect the brown wire ends of your cable assembly to a bulb socket (picture #5).
4. Fill the gap between bulb socket and your cable assembly with some hot glue as a kind of makeshift strain relief (picture #6).

Tadaa, you’re done!

You can now test the pedal and the cables with your new simulator – just connect first the pedal cable to your custom female connector, then the machine cable to your custom male connector, insert a 60 to 75 Watt lightbulb into the socket, and finally plug the other end of the machine cable into a wall outlet.

If the cables and the pedal are ok, you can turn the lightbulb on/off and dim it using the pedal, as shown in the video below.

If the pedal is faulty, there are several possibilities:

1. The simulator’s lightbulb is always ON. In this case, when plugging the cables to the machine instead of to the simulator, the machine immediately starts running at full throttle – then most likely the capacitor in the mechanical pedal must be replaced. It is possible that the pedal produces a nasty smell, gets very hot or starts to smoke. If the capacitor isn’t the culprit, then I recommend replacing the pedal, see step 5. Please note that when using a mechanical pedal for an extended time, also in normal operation it can become warm, but it will not produce any smoke signals or other olfactory effects.
2. The simulator’s lightbulb is always OFF. In this case, when plugging the cables to the machine instead of to the simulator, the machine will not run regardless of the pressure on the pedal – then most likely the pedal is faulty. Faulty pedals can be repaired, but it is a bit tricky; in such a case I recommend replacing the pedal, see step 5.
3. The simulator’s lightbulb is ON and OFF alternately when moving the cable(s) around. In this case, when plugging the cables to the machine instead of to the simulator, the machine will sometimes run or stutter, and sometimes it won’t – then most likely somewhere along the cable’s length there is an interrupted wire, usually close to one of the connectors. You can try to locate the interruption by intentionally wiggling the cable. For repairing interrupted cables, see step 6. There also could be a slack joint inside the pedal, in its mechanics, or its graphite column. As I said above, repairing pedals is a bit tricky; in such a case I recommend replacing the pedal, see step 5.

The not-so-very-different diagrams for machine simulators of the version 2 and 3 types are given above, too, followed by a picture of some more custom connectors/simulators from my own production for different sewing machines, from left-to-right:

1. The simulator for 530- and early 730-type Bernina machines. This is the one for which I gave the step-by-step instructions in step 3.
2. The simulator for later 730-type Berninas.
3. The simulator for 802-803-type Berninas (as you possibly can see, this is first one I made and the ugliest of them all).
4. A little off-topic: Adapter for connecting an aftermarket pedal to the pedal cable connector of the 803-803-type Berninas. In fact, only two of the three pins of the adapter plug are used.
5. And the last one at the far right, again a little off-topic: Simulator for a Singer 8280.

This is my little family of sewing machine pedals – from left to right:

1. The mechanical LWA-43/2 pedal for the early Bernina 530 Record, Swiss-made by Scintilla SA (I think also the early Bernina motors were purchased from Scintilla).
2. A much more modern, cheap, mechanical ‘horseshoe’ pedal (https://www.amazon.de/N%C3%A4hmaschinen-Fu%C3%9Fpedal-Hufeisenf%C3%B6rmiges-EU-Stecker-Universeller-Empfindlicher/dp/B0CDHZW4BZ/ref=pd_ci_mcx_mh_mcx_views_1_image). There are several retailers selling via Amazon, but the machine connector of none of them matches any Bernina machine – so you have to connect the cable from the pedal to your original Bernina pedal cable by yourself.
3. A modern, cheap electronical pedal (https://www.amazon.de/ckpsms-Marke-325-213-14-FUSSBEDIENPEDAL-N%C3%A4hmaschine-830-831-800/dp/B07YD1GJM9/ref=sr_1_7?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&sr=8-7). There are even versions with a machine connector fitting the Bernina 830-series sewing machines. You can, however, connect the cable from the pedal to your original Bernina pedal cable by yourself if you have a different type of machine.
4. And the one at the far right is my own, DIY sewing machine pedal. I made it using a Proel GF12L guitar volume pedal. It contains nothing but a potentiometer and a very simple, very convenient dimmer module by Conrad. But at the end of the day all the components cost me more time and money than any of the two replacement pedals above.

These pedals all are specified for 220/230 V mains voltage. If you live in a 110/115 V country, be careful to purchase a replacement matching your local mains voltage. The two links above are, of course, only valid at the time of writing, they can be dead tomorrow or the day after. But I'm confident that you know how to use Amazon's search function.

When buying a replacement pedal from Amazon or, e.g., AliExpress, make sure that you really get what you want before you click on the 'buy' button! Many sellers, not only from China, either don’t really know what they sell, or they trip over the language barrier – the amount of nonsense you can find in many of the product descriptions is amazing. So, caveat emptor! (in plain English: Buyer beware!). Sending back an item that doesn’t really match and getting a refund is rather easy with Amazon, but next to impossible with a Chinese seller – and can become quite expensive, at that.

Connecting the two-wire cable from the pedal to the sewing machine’s original pedal cable is no rocket science – except in the case of the three-wire, version 3, pedal cable. There you have to be careful to pick the two correct wires for the connection - one helpful hint to do so is given at the end of step 2. When connecting (‘splicing’) cables, make sure that the contact is mechanically solid (e.g. by twisting the two wire ends around another and then soldering), and that the two wires are insulated from each other and from the outside world, e.g. by using heat-shrink tube.

This step is not exactly the main focus of this Instructable and still is work in progress, I apologise for that. It will be updated as soon as it is finished. Thanks for your patience!