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This is an old timer used in public safety vehicles. It is no longer in production. Some coworkers have hinted for some time that they'd like to be able to recreate it because it's been such a solid device for so long and they don't want to move to a different device. I have downtime, so I'm taking it on. 


The DIP switches on the bottom right are intended to change how long the device stays "on", allowing equipment in the vehicle to remain powered. R12 and R13 were added by me after reading through the tutorials. The battery and igniton are both 12V, but the ignition is the trigger so I changed it to a pulse function. I tried changing the battery to a pulse too, just to see and didn't see much change. R9 is the load I created to see if the relay was working. It's a T9AS1d12 12V automotive relay from Potter and Brumfield. I was able to find that model in the spice library that, according to EasyEDA's documentation had a spice model but it didn't seem to work, so I changed it to the current one. Which also doesn't work. I had R9 connected to pin 87 and moved it to 87A when I didn't get an output, which I still don't on 87A. 


I'm confident my tracing is correct and I've done my best on components. What I'd like to do is simulate the circuit and see if modifying the switch resistors, capacitors and IC will give a more accurate time range. For example, switch #5 on the device is labeled as "1 to 3 hours" of run time. That seems like a wide margin. The voltage probe C1 shows a ramp up to 12V which is what I would expect, but if I close a switch the voltage is very low, which is what I would expect after some time, but there aren't any transients or anything that shows me info up until that point. 




DK Timer Original

Andy Fireman Rework B

Andy Fireman Rework A

DK Timer Rev A


ID Name Designator Quantity
1 1N4148 D2,D1,D3,D2,D1,D3,D2,D1,D3,D3,D2,D1,D2,D1,D3 15
2 74HC00 U1 1
3 PWL(0,0, 100m,0, 101m,12, 1000m,12, 1001m,8, 2000m,8, 2100m,12, 3000m,12, 3001m,0) V_IGNITION1,V_IGNITION1,V_IGNITION2,V_IGNITION1 4
4 AND2EE U1,U1,U1,U1 4
5 PULSE(0 12 1m 1 100m 16000000m) BATTERY 1
6 PULSE(8 12 100m 1m) IGNITION 1
7 PULSE(12 8 1001m 1m 100m 999m) V_BATTERY1,V_BATTERY1,V_BATTERY2,V_BATTERY1 4
8 SPST_Open S6,S4,S3,S1,S2,S5,S6,S3,S1,S5,S1,S3,S4,S5,S7,S2,S1,S3,S4,S5,S7,S6,S6,S4,S3,S1,S2,S5 28
9 SPST_Close S8,S2 2
10 10K R8,R10,R6,R6,R9,R2,R8,R10 8
11 1.2K R9,R10,R10,R3,R9 5
12 100 R7,R7,R7,R1,R7 5
13 1G R11,R11,R13,R12,R11 5
14 1Meg R2,R2,R4,R2 4
15 16Meg R6,R6,RTIMER1,R8,R6 5
16 6.2Meg R5,R5,R7,R5 4
17 4.5Meg R4,R4,R6,R4 4
18 2Meg R3,R3,R5,R3 4
19 400K R1,R1,R1 3
20 2M R2 1
21 4.5M R3 1
22 6.2M R4 1
23 16M R5 1
24 18M R8 1
25 1M R1 1
26 1K R9,RLOAD,R11 3
27 18Meg R9 1
28 10G RC1,RC2 2
29 10 R14 1
31 2N2222 Q1,Q1,Q1,Q1,Q1 5
32 Relay U2 1
33 1000u C1,C1,C1,C2,CTIMER1,C1,C2,C1 8


Filename Download
Switch Open.png
Switch Closed.png


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