K2579 Timer duration

I have two of the K2579 Timer modules and have correctly built the boards and checked all the components but I cannot set the timer to a duration of greater than 5 minutes, the kit should have a duration of 15Minutes as standard - any ideas.

Due to capacitor tolerances, it is possible that the time is less.
In that case, increase the cap. value. Sorry, no values, please experiment.

I have been wondering about the maximum output time as well as all datasheets I have seen from any 555 manufacturer all give the monostable output time as 1.1 x RC. With the values of 2M2, 1k, and 100µF in this kit this formula results in a theoretical maximum time of 242 seconds, or 4 minutes and 2 seconds.

I have noticed that you have adjusted the Control Voltage with R2 and R3, but only ever so slightly as the internal resistors are the equivalent of 10k and 5k versus 10k and 4k7 for the external resistors, so I don’t expect this can extend the output time by that much.

Can you reveal the secret? :wink:


This kit has been marketed as-is for almost 30 years without any problems.
Due to the age, there are no circuit descriptions or other details available.

I’ve just bought this kit for a timer project, however I’m having the same difficulty as paulgorton and many other forum posts in that I can only get the timer to operate for about 6 mins.

Your documentation is misleading as the front page of the instruction manual states ‘up to 60 minutes delay’, but doesn’t indicate that modification is necessary until the ‘hook up and use’ section of the manual which would be after customers have bought and built it.

Capacitor tolerances might affect the timing however as all the other posts I’ve seen suggest that the specified 100uF capacitor is only capable of between 4-7 mins so tolerance differences may only determine where in that range the timer duration would fall, maybe you should be including a larger cap in the kit to at least meet the 15mins minimum?

As you’ve been producing these kits for 30 years or so, in pursuit of better customer service, why not have one of your engineers build one, test a range of capacitor values and publish a table showing cap value vs max time - it would be much more helpful than ‘Sorry, no values, please experiment’?

Your second comment about it being marketed for 30 years without problems is just dismissive and customer un-friendly, by the way, the circuit diagram is on page 11 of your instruction manual?

In summary, the kit is a good basic timer, it may need to be modified to meet some of your customers requirements, you should consider assisting your customer base by providing an addendum or a note on the forum detailing what value caps would provide an estimated maximum time.


I think it’s really poor that Velleman didn’t respond to my comments about being more helpful and customer oriented, it seems that poor customer service is the norm rather than the exception in todays world of commerce. However I did try a bigger cap and wanted to post some info for other purchasers of this kit.

I read somewhere else that a 1000uF cap gives about 15 mins so as I need about 30 mins, I looked for something around 2000uF but they were expensive, the best option I found for about £1.60 was a 4700uF 25v Electrolytic and having replaced the inadequate 100uF my first test was very successful.

At full throw of the adjustment pot, I got at least 90 mins (I got bored of waiting) before stopping it, so although I don’t know the full delay it should be sufficient for most projects, the only trade-off is the size of the capacitor vs the original 100uF.

I’m now trying to adjust for about 30mins, I seem to recall from my electronics student days that potentiometers are logarithmic so have started with the pot wound to about 30%.

Good luck with your own experimentation.


je suis d’accord avec autopia,

  • la documentation est éparpillée et incomplète,
  • le timer annoncé 15 minutes fait maximum 4 minutes sur celui que je viens d’acheter, et visiblement je ne suis pas le seul !
  • la sensibilité est trop grande dès que l’on déporte les boutons, le signal est trop facilement parasité
  • un produit qui a 30 ans et qui n’a pas évolué.
  • les relais de sorties qui équipent ces kits sont un peu limites, sa puissance annoncée imprécise, tantôt 2A tantôt 3A.

On trouve aujourd’hui sur ebay ( 12V Power-OFF Delay Relay Module Delay Circuit Module )des cartes déjà montées, plus fiables, modernes et précis, avec des composants de surfaces, et surtout proposant plus d’options, par cavaliers ou switchs et le tout pour moins cher.


Je possède ce kit aussi,vous parlez de découplage HF pour l’alimentation.
Ou puis je trouver ce circuit?
Proposez vous un schéma, un kit?


En principe, il n’y a pas de problèmes, si vous utilisez une alimentation classique avec transfo et si vous laissez les boutons-poussoirs sur la platine.


Justement les boutons poussoirs seront à plus de 1 m !
J’utilise une alim. sans transfo.


Dans ce cas, il vaut mieux choisir le VM141