The cHipp Toggle clock

A DIY, free pendulum, electrical master clock project.


Inspired by Matthias Hipp's idea of 1842.

What is the Hipp Toggle ?

If an unpowered clock pendulum, is set to swing, it will describe an arc that will slowly decline in amplitude. The decline is affected by three interferences.

1) the suspension on which it hangs. This is usually a spring
2) The resistance of the air through which it passes. This varies with barometric pressure.
3) Any interference to it motion that occurs during its arc of swing. This may be mechanical or magnetic.

Matthias Hipp's original Hipp toggle was a simple metal toggle attached the the side of the pendulum rod that closed a contact when the arc of swing fell to a certain minimum amplitude. It then momentarily powered an electro magnet as the Pendulum passed through "zero" or bottom dead centre. This impulse accelerated the pendulum slightly on that swing. The arc increased and the Hipp toggle effect would not be invoked again until the amplitude had again fallen to the set amplitude.

The clever bit is that the pendulum is subjected to the minimum of mecahnical interference over significant time intervals - often 30 seconds or more.

Matthias Hipp proposed this idea in 1842. Below is Frank Hope-Jones description of the Hipp toggle. It's reproduced from his 1949 book "Electrical Timekeeping". Frank Hope-Jones was the designer and manufacturer of the 20th century Synchronome master clocks (which did not utilise the Hipp toggle)

....But one cannot speak of merit in electric clock inventions without giving pride of place to the Hipp "Butterfly" escapement which is illustrated in fig. 37. An apparently free /pendulum has an armature attached to its lower end above an electro-magnet fixed to the case. The pendulum carries a little freely swinging vane. This vane trails backwards and forwards over a notched block mounted on the end of the upper spring of a pair of contact springs until, as a result of the gradually decreasing arc, it engages the notch and forces the top spring vigorously into contact with the lower. The notched block, or the electro magnet, is placed a little off-centre, and the contact is so adjusted that the attraction takes place at the correct phase of the pendulum's vibration, the optimum position for increasing the arc and causing the vane to trail over and beyond the notch until the action is called upon to repeat itself.

Also: Observe that, though fluctuations of battery power vary the value of the impulse, nevertheless the frequency of the impulses is increased automatically and in exact proportion to their lack of strength; hence the average arc is reasonably constant.
A further outstanding merit of the invention is the comparative freedom of the pendulum, due to the wide intervals at which contact and 'impulses take place. Add to this the concentration at zero of such interference as exists, and
you get such a good timekeeper that it was actually tried in observatories for precision purposes.

You must read Frank Hope-Jones's interesting book for more.

The Hipp Toggle principal was not widely used but the British Post Office used it in their telephone exchange clocks master until as late as 1980. There is a good explanation of the Hipp Toggle Post Office No. 36 clock at . If necessary have a look ; It may help understand what follows.

My Clock

I had wanted to make a pendulum clock of my own for a long time. It was always going to be largely electronic because my mechanical skills are not great. My inspiration came from the master clocks with one second pendulums that were so popular in large buildings during the first three quarters of the 20th century. The Synchronome clock designed by Frank Hope-Jones being one of the best. The story of other clocks I have is HERE

The time keeping of the Synchronome clocks - claimed to be within 2 seconds per week - would be the standard I would aim to achieve.

I have never been an proper horologist so my "bible"has been the book referred to above and I have tried to abide by the important priciples outlined by HJ. There are other electrically maintained pendulum clock ideas to be found on the internet and no claim is made that this scheme is any better than the others. It is just an interesting experiment in basic electronics and horology.

My "toggle" effect is produced with opto-interupters, rather than mechanical devices. When the infra-red beam which passes between the two small pillars is broken by a passing object, an output pulse is generated for as long as the beam is broken. The type I used have a comparator chip on a small pcb and were sourced cheaply from eBay. (as low as 99p)

A short length of soft sleeving which I will call the "flag" is attached to the 4ba rating thread beneath the bob so that it passed between the the pillars of three opto-interupters as the pendulum swings back and forth, creating the operating pulses as it passes. Soft rubber sleeving is used to prevent damage if the flag accidentally hits the arms of the opto-interupter.

The optos are arranged from right to left in the order A, B, C. When the pendulum is stationary the flag hangs midway between optos A and B - ie. at Bottom Dead Centre (BDC). An important point is that the electro magnets are co-incident with opto A; slightly to the right of BDC.

When the clock is running, as the pendulum swings from its rightmost extremity, it first passes through opto A, then B generating a short pulse from each one as it goes. A and B are 0.5" apart, centralised on BDC.

Opto C is positioned 3/4" to the left of BDC and is the Hipp Toggle sensor. It works like this. Assume the pendulum has sufficient amplitude to swing right through opto C at its leftward extremity. A pulse is generated. It then stops and begins to swing back to the right. As it does it passes through C again, generating a second pulse.

So on every swing that has sufficient amplitude to pass through opto C twice, two pulses are generated in quick succession. These are fed to a cmos counter chip (CD4013, a) which is wired to divide by two. In other words the output of the 4013 counter is clocked HIGH then LOW.
This is the digital equivalent of the toggle in the mechanical version passing over the V block.

All the while the pendulum arc is slowly decreasing and eventual (now, after 52 seconds in my clock) there will come a time when the flag does not pass right through opto C but enters it, reverses, and proceeds to the right again generating only ONE pulse. This will clock the counter HIGH and and it will remain HIGH as returns to the right. This is the equivalent of the mechanical vane catching on the V block in a mechanical Hipp Toggle clock.

Then as the pendulum continues its swing back to the right it passes through opto B (1/4" from BDC) generating another pulse. A basic chip known as a NAND GATE (IC3a, CD4011) detects that it now has two HIGH signals on its input terminals - one from opto C which was left in the HIGH state and a HIGH from opto B as the flag arrives. With these two HIGHs on its input its ouput goes LOW, is inverted in IC3b to make a HIGH which triggers a flip flop (IC2b) to HIGH which remains HIGH until the flag passes through opto A which resets it again to LOW.

Thus the HIGH on THIS flip flop (ic2b), as the pendulum travels between opto B and A, is the drive period control for the electro magnet's drive pulse. This drive pulse is switched on with a transistor and the Electro-Magnets are powered during that section of the arc (B>A) giving the pendulum an impulse which maintains the pendulum in motion.

On the next swing the pendulum will again pass right through opto C because of the slightly increased swing amplitude and the process will repeat in as many seconds as the energy given by drive pulse will allow. (now 50 seconds in my clock)

A feature of this design is that the pendulum arc is closely controlled by the position of opto C relative to BDC. ie. .75" This works out to be about 1.9 degrees or 0.95 semi arc. This is quite a small arc which is good for time-keeping and the system has been so reliable that an even smaller arc might be entirely possible.

Here's a short video showing the pendulum as it was in an earlier implementation when the "flag" was in front of the bob which was a serious mistake because axial rotation of the bob introduced errors. The LED on Opto C can be seen to blink twice until, after about 30 seconds, it only blinks once (circled). A drive pulse is generated as described above. Please note that sometimes the quickest of the double blinks appear a single blink due to the frame rate of the video.

The circuit of the electronic cHipp Toggle section.

The purpose of Ic1 (6x Schmidt trigger inverters) is to speed up the pulse edge transitions from the opto-isolators. Used in pairs,the original pulse polarity is maintained.

The completed electronic cHipp Toggle unit

We now have a drive pulse positioned 1/4" either side of BDC which, when amplified by the transistor switch, powers the EMs for 220 milliseconds; that period being set by the distance between opto A and B.

Frank Hope Jones in the Synchronome clock, powered his pendulum at fixed 30 sec intervals with the potential energy of a gravity lever hanging up on a catch so that the energy imparted as the bob passes through BDC was always the same.

The pendulum impulse in this clock is delivered magnetically to the armature beneath the bob. The force of attraction of a magnet varies as an inverse square law of the decreasing distance to the approaching armature.

In my clock, the energy that pulses the EMs does not come directly from the battery but from a capacitor charged to precisely 5 volts from a voltage regulator. This ensures that exactly the same energy is available on every impulse. The capacitor value was found by trial and error to empty its charge during the 220 millisecond period that the drive is energised. Because of the capacitor the current through the EMs decreases exponentially over the 220 millisecond drive period.
Without the capacitor, as the distance to the EM decrearses, the effect of the magnetic attraction would increase as the square law..However the magnetic field is decaying exponentially due to the discharging capacitor and (it is hoped) the two effects will produce a roughly steady accelerating force on the bob. The interference on the pendulum is now occurs only for 1/250th of its running time anyway.

The oscilloscope image below shows the falling voltage applied across the drive coils during the 220 milliseconds pendulum drive period. A side effect of this system is there is virtually no back EMF generated when the swicthing period ends, so protection of the switching transistor is not needed.

Due to inductance, the current waveform is slightly different..In particular it has a slower rise.

The armature beneath the pendulum is of low remnance steel taken from a GPO relay. There are no fixed magnets in this design.

Here is the circuit diagram of this "capacitor drive" section.
(this is a scan of my own notes so the pin numbers etc are not relevant)

How it works. The Qbar output of ic2b in the Hipp toggle circuit , which is normally HIGH, is connected to the input (i/p) on the left. This turns on 2n3906 transistor which in turn turns on the 2n5193 pnp transistor above. TThe 3300uf capacitor is charged quickly to 5 volts exactly . The 5 volts comes from the 2940-5 low drop out voltage regulator (2940-5).

When the cHipp Toggle circuit calls for a pendulum impulse, Q of ic2b turns on the EM's drive transistor (lower right), At the same instant Qbar goes low , removing the 5 volt feed to the 3300uf capacitor. The capacitor is now the only source of current for the EMs during the drive pulse period. (220 Milliseconds)

* the 16ohm and 33ohm resistors in the electro-magnet circuit were adjusted to achieve a time between impulses of about 30 seconds. Later the period was changed to over 50 seconds.

The clock

The pendulum rod comprises a 1 metre length of 8mm Invar, extended with a short length of steel and steel 4Ba studding to make the required length.

The pendulum's arc of swing is determined entirely by the spacing of the opto-interupters and is, on average, just 1.9 degrees. (.95 semi-arc)

The pendulum is about a "free" as a pendulum can be without being enclosed in a low pressure tank. (as in the Shortt / Synchronome clock)

The mahogany case came from a clock related junk shop in Brixham.(Now sadly gone !) It has been modified and varnished. It may have been easier to start the case from scratch.

The pendulum is suspended on an oak bracket and the top chops are similar to those used by Gents and the GPO No.36 clock – two penny washers and a length of threaded rod. A piece of .005” feeler gauge stock serves as the suspension spring.

Initially he pendulum bob was a brass shell case with a coil of 6” wide lead inside which was left over from the lead flashing when I built my workshop a few years ago. Before final assembly a length of steel pipe was added and polyester resin partly filled the space remaining to stabilise the whole. The final weight was 6Kg. But in May 2016 this was changed to a steel bob 8" tall x 2" diameter weighing 6 lbs.

The picture below (left) shows the pendulum stationary at BDC and the magnet drive assembly. The the optos interupters are behind the black plate, The electro magnets were taken from an old buzzer.

In spite of the small black shields, direct sunlight falling on the clock can upset the operation of the opto-isolators, therefore the clock needs to be positioned where the sun cannot directly shine on it.

The dial mechanism is a Gents 1 second, alternate polarity unit with a silver effect dial card printed on a PC printer.


Drive magnets and optos behind the plate
Oak pendulum support and chops

The cHipp Toggle clock has no friction other than that of the suspension spring and the air through which it passes. It has a very small arc which is tightly controlled so circular error has virtually no impact. The is no escapement to interfere with the motion of the pendulum except for the precisely controlled impulse which are now every 50 seconds. Temperature control by Invar rod must equal that of the gridiron pendulum and, anyway, the temperature control in a centrally heated home does not allow the wild variations experienced 100 years ago when such clocks were the norm. Therefore I am tempted to believe that an electrically impulsed clock of this type might be as good a pendulum clock as can be constructed whilst running in free air. Only the often mentioned quartz rod pendulum rods might offer a small improvement.

It was Frank Hope-Jones's Synchronome clock system (and his previously mentioned book) that inspired me to make this clock. One of the advantages of the Synchronome system is that the current consumption of a Synchronome clock is miniscule whereas any electronic clock has a continuous drain. Of course, in a modern quartz clock this drain is reduced to a tiny current but the cHipp toggle clock is drawing 90 Ma continuously because of the three opto-isolators, LEDS indicators and the electronics.

This is not much of a problem as I've used a trickle charged 6 volt lead acid battery in case of a power cut.


I have made a start on a second clock. This will use the case of a PO No36 clock and the chassis of an "ME Jubilee electric clock" I've no idea yet what principles will be employed

I have also bought two more Synchronomes one of which ( a late MK2) has two BO22439-3 printed circuit boards which send alternate polarity drives for half minute and one second dials. Work is in progress to trace out the circuit diagram. These boards must be rare as their is no published information on the internet - or a mention in the Synchronome bible by Miles. Please email me if you have any info on these boards.


Originally the clock was fitted with a Synchronome dial mechanism that required an impulse every 30 seconds. This was taken from opto B and a simple divider circuit included to make the impulse every 30 seconds. This has now been didpensed with and it's now fitted with the Gents, silent, seconds indicating, alternate polarity slave clock mechanism mentioned in the introduction. The dial motor resistance is 3.4 ohms and the required drive current is 220Ma. The dial was printed on silver card with a laser printer.

Clock dial, July 2016

Pulses from optos A and B are "or'd" and inverted in ic3d (circuit above) and fed to the circuit below.


Alternating polarity pulse driver for the Gents low voltage, silent dial mechanism.

The incoming double pulse is converted to a single pulse of about 220 milliseconds duration with a period of one second by 4013a (ic3a). This is divided by 2 in 4013b. The two opposite phase (Q & Qbar) phase outputs are gated with the single pulse to produce positive going pulses of 220 milliseconds duration alternately, to drive the H-bridge. It was just luck that the spacing of Optos A & B were 220 Milliseconds apart and that the pulse resulting at 4013b i/p was a suitable length to drive the Gents dial movement.

H-bridge module with one pound coin.

The gem in this circuit is the tiny H-Bridge module sourced from ebay for a mere 99p post paid. Rated up to 10 volts and 1.5 amps its more than adequate to drive the dial motor. Pictured above with a £1 coin for scale, it features two H-bridges, so a couple of additional series dials could be run separately from the B output.

The steady current consumption is now 100ma - mostly due to the LEDs in the Opto-interupters and the other indicators.

How well does it work ?

The clock is capable of keeping extremely good time. The temperature compensation is not perfect and has not been adjusted on test. There are still short lengths of brass (top suspension) and steel (suspension spring, 1.5 inches steel making up the shortfall of the 1 metre Invar rod and the 4 Ba rating thread) which could be compensatated for in some way. The bob expands upwards and will compensate to some extent to the downward expansion of the parts listed above - albeit at different rates due to their mass.
The clock case is insulated inside with 10mm of polystyrene.

The effect of changes in barometric pressure are also seen - as in any pendulum clock, unless barometric compensation is incorporated. The ultimate solution is to enclose the pendulum in a low vacuum enclosure, as in the Shortt/Synchronome clock.

In the initial trials I found some variations in rate which were difficult to explain and the following mechanical improvements were made.
The sliding fit of the bob on the rod was made near perfect.
Axial movement of the bob on the rod was eliminated.
The Rating Nut was replaced with a pair of standard lock-nuts.
Great care is required when regulating an accurate pendulum clock. Fine adjutsments of rate now require small weights to be placed on the top of the bob. With a 6 lb bob I've found it neccessary to have weights available down to 0.1 grams to achieve suffucient accuracy.

The constrction of the clock has been an on/off process over 2 years. During that time I've been lucky enough to make the aquaintance (online) of a chap who has written a program for the RaspberryPi (mini computer) that can monitor and record the going of a clock in remarkable detail. Originally designed for the Synchronome system it accepts and records the timing of the 30 second pulses against internet time (NTP) I've used the divide by 30 board which formed part of my clock in its first configuration to feed the Pi monitoring system.

Here is a graph of the last week of running which shows that it has kept well within +/- 0.5 seconds during that period. The small gaining and loosing periods exactly agree with the variations in pressure which occured.

Wednesday 31st May to Thursday 8th June 2017

The vertical scale of this graph is +/- 0.5 seconds. The loosing rate on Wednesday 31st was corrected in the afternoon with a small weight adjustment. Slightly high pressures predominated until Sunday when low pressure arrived. At end of the period shown the pressure was 1001 Mb - about 12 Mb below what I think is the mean pressure here.

last updated 08/06/2017

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