2 stage timer circuit

[airasolt]

I am trying to design a two stage timer circuit using off the shelf components which I have already chosen. The idea is simple. The first stage is a digital display countdown timer that triggers the second stage. The second stage timer is a fixed run time timer module. The second stage is triggered with a momentary or continuous connection of the "on" terminals. The "on" terminals are voltage isolated from the module. It is commonly called a single shot timer.

Both timers operate on 12VDC.

Here is the problem. The first stage timer has relay contacts that are closed when the timer is running or "counting down", the contacts are open when the timer is on standby or powered off. When the countdown is completed the relay contacts open. I need the first stage timer to do the opposite. When the "countdown" is finished (the delay) I need it to signal the second stage timer to start with either a momentary or continuous connection. The problem I had when trying to connect another relay to the first stage timer (to get the proper contacts) is that it would trigger when I initially powered on.

 

[blueroomelectronics]

How did you choose the parts without a design?

 

[Mike_2545]

The problem I had when trying to connect another relay to the first stage timer (to get the proper contacts) is that it would trigger when I initially powered on.

so what is the problem?

 

[airasolt]

I chose the parts because of their availibility and cost. I don't have a design because I am an amateur with limited knowledge. I know what I need this to do and figured I could back my way into it. This will be replacing an old electro-mechanical timer in a piece of equipment we manufacture.

The problem is that the second stage timer turns on with out the benefit of the countdown delay because the added relay is not powered on before I plug it in to the wall socket. There is enough of a momentary pulse to turn on the second stage.

Thanks
Scott

 

[Mike_2545]

Is the first relay spst or spdt? If not change out the relay...

 

[blueroomelectronics]

Might be helpful to list what parts you're planning to use plus schematics.

 

[airasolt]

It is a spst. That's the problem. The unit is closed, panel mounted, easy to use and fits into our budget. I see no easy or cheap way to swap out the relay. How can I do it externally of the unit.

I'll be away for two hours.

Thanks
Scott

 

[airasolt]

Here are the links for the two timers:

Dwyer Instruments - Series LCT316


Single Shot Products

In addition I have a 12VDC power supply.

I just need to hook them up so the countdown timer (dwyer) triggers the single shot timer module (airotronics) when the countdown timer reaches "0". This will allow a variable delay in the start time. Then the timer module would run for it's preset time. Perfect, except the countdown timer doesn't have the proper relay contacts. There must be a simple solution but I am to inexperienced to figure it out. I have a variety of relay boards here if they would help.

Thanks
Scott

 

[airasolt]

I've posted a reply with the links to the components. The moderator has to approve it. I don't know how long that will take.

I am grateful for your ideas and any help you can give.

Thanks
Scott

 

[airasolt]

On the link above link for "single shot products" The module that I'm using is the "TGP" series.

Thanks
Scott