# Three Step Sequence Without An IC?

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#### LoTek

##### New Member
Hello, I'm new to the forum. I've been poking around and there seems to be a lot of great info here!

Maybe you guys can help me out with a project. I am attempting to construct a two, three, or four-step sequential circuit without the use of IC's (555, CD4017B, etc.). Maybe something using SCR's? My goal is a cascadable time delay circuit for automotive turn signals. I did a search and found some good info but not exactly what I am looking for.

Here is how I envision it working:

• Application of +13.6VDC illuminates 1st lamp
• Delay
• SCR 1 triggers, illuminating 2nd lamp
• Delay
• SCR 2 triggers, illuminating the 3rd lamp
• Etc.

All illuminated lamps should stay on until voltage is removed from the circuit. When voltage is removed lamps should go off immediately.

Example of lamp to be used: 1157 automotive bulb.

I want to keep the circuit a simple as possible (without the real estate required for 555 timers and decade counters).

Any help will be greatly appreciated.

#### Russlk

##### New Member
Try this circuit:

#### Attachments

• SEQ_CKT.jpg
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#### LoTek

##### New Member
Thanks! :mrgreen:

I knew I was making it harder in my own mind than it had to be.

I'll pick up the parts and try it out tomorrow.

#### LoTek

##### New Member
Russlk - I can not locate the SCR you have listed (Teccor S1004DS1). Teccor themselves do not list it (on their website). What were the specs you had in mind?

Do these values strike you as sufficient?
• Vdrm = 600V
• Vrrm = 600v
• It(rms) = 5A
• It(av)=3.2A

Anyone have a suggestion for a sutible substitution?

#### Sebi

##### Active Member
For 13,8V application quite enough 50...100V Vdrm. Just It(av) must be higher as lamp amperage.

#### Roff

##### Well-Known Member
LoTek said:
Russlk - I can not locate the SCR you have listed (Teccor S1004DS1). Teccor themselves do not list it (on their website). What were the specs you had in mind?

Do these values strike you as sufficient?
• Vdrm = 600V
• Vrrm = 600v
• It(rms) = 5A
• It(av)=3.2A

Anyone have a suggestion for a sutible substitution?
Teccor has the S2004 in a couple of different packages, if I recall correctly. It has a maximum gate current of 50ua, which you will need in this application. I think it would be better to connect the capacitors from gate to cathode instead of ground. Connecting them to ground will reverse bias and break down the gate junction on each cycle. I don't know if the low current (~100ua) is destructive, but I wouldn't take the chance.

#### Russlk

##### New Member
The previous replies are both correct, I chose the SCR from the Teccor website because of it's ratings: 100 volt, 4 amp, 50 uamp gate current. Any equivalent should work.

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